Optical head used for recording on optical recording medium having various thicknesses, warpage and the like

ABSTRACT

An optical head apparatus includes a stationary optical system having a light source and a detector for detecting light reflected by a recording medium, which stationary optical system is arranged at a position fixed to the recording medium. Plural objective lenses for focusing/irradiating light emitted from the light source onto the recording medium are arranged on a rotating blade which is provided to be rotatable in a direction parallel to the recording medium. By controlling the waveform of a current to be supplied to a tracking coil, the blade is rotated and a desired one of the objective lenses is located on an optical axis of the light irradiated onto the recording medium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical data recording/reproducingapparatus for recording/reproducing data in/from an optical datarecording medium such as an optical disk and, more particularly, to anoptical head used therefor.

2. Description of the Related Art

A technique of reproducing data recorded on an optical disk byirradiating a light beam on the optical disk and detecting lightreflected thereby is widely used for a CD (Compact Disk) apparatus, anLD (Laser Disk) apparatus, and the like. In such an optical diskreproducing apparatus, a light beam emitted from a light source such asa semiconductor laser is focused/irradiated on the recording surface ofan optical disk via an objective lens, and light reflected by theoptical disk is detected by a photodetector, thereby reproducing datarecorded on the optical disk.

As attempts have been made to increase the recording density of opticaldisks, optical disks have been developed on the basis of standardsdifferent from those of conventional optical disks. For example, thesize of a pit as a unit in recording data is about one micron atpresent, but it is highly possible that the size of a pit is reduced toa value on the submicron order.

The recording density of an optical disk is determined by the size of abeam spot for a recording/reproducing operation, which is irradiated onthe optical disk by a pickup (optical head) to read a very small pitformed in the optical disk to record data.

The size of this spot is determined by the wavelength of a light beamemitted from a laser used and the NA (Numerical Aperture) of anobjective lens, and is given by

    spot size=k×laser wavelength/NA

where k is a constant.

When, therefore, data is to be read from an optical disk having a higherrecording density by using a small spot, a laser having a shortwavelength or a lens having a large NA must be used.

A conventional data recording/reproducing apparatus is designed to haveonly one objective lens. For this reason, data cannot be read from ahigh-density optical disk by using a pickup having an objective lenscorresponding to a conventional optical disk.

More specifically, assume that a pickup for a high recording densityuses an objective lens having a large NA. In this case, if an opticaldisk tilts with respect to the objective lens, the disturbance of a spotis large. For this reason, the pickup cannot be commonly used forconventional and new optical disks in many cases. That is, the allowablevalues for, e.g., the warp of an optical disk are large according to theconventional standards, but those for a new optical disk are small.Consequently, data cannot be read from an optical disk having largewarp.

Note that the disturbance of a spot is influenced by the thickness of anoptical disk. With a decrease in the thickness of an optical disk, thedisturbance of a spot is reduced when the optical disk tilts. For thisreason, a thin optical disk is used as a substrate for a high-densityoptical disk in some case.

With respect to the same optical disk, different specifications may beset for optimal objective lenses in a recording operation and areproducing operation, respectively. Since a conventional apparatus hasonly one objective lens, the apparatus cannot cope with such a case.

In addition, according to new standards, there are disks havingsubstrates which are different in thickness from each other. For thisreason, it is possible that a new apparatus cannot record or reproducedata on or from a disk based on the conventional standards.

Consider the thickness of a disk substrate as a standard. An opticaldisk of this type is generally designed such that a reflecting film isformed on a transparent substrate (to be referred to as a disk substratehereinafter) on which data is recorded in the form of pits, and aprotective layer is formed on the reflecting film. A light beam isirradiated from the disk substrate side onto the reflecting film as arecording surface. In this case, the reproduction characteristics changedepending on the thickness of a disk substrate. FIGS. 1A and 1B showchanges in transmission wavefront aberration with tilting of opticaldisks with respect to an objective lens. FIG. 1A shows a case whereinthe thickness of a disk substrate is 1.2 mm. FIG. 1B shows a casewherein the thickness of a disk substrate is 0.6 mm. As is apparent fromFIGS. 1A and 1B, even with objective lenses having the same NA, thetransmission wavefront aberration caused by a disk tilt is smaller inthe thinner disk substrate, and a focused spot on the recording surfaceexhibits good focusing characteristics. Consequently, a reproductionsignal having good quality can be obtained with the thinner disksubstrate. For this reason, an optical disk apparatus using an opticaldisk having a thin disk substrate has been developed. As optical disksconstituted by disk substrates having different thicknesses aredeveloped, there naturally arise demands for reproducing data from theseoptical disks by using the same apparatus.

In some apparatuses proposed (e.g., Japanese Patent Disclosure (KOKAI)Nos. 4-372734, 5-266492, and 62-66433), a parallel flat plate isinserted between an optical disk and an objective lens to properlyreproduce data recorded on a plurality of types of optical disksconstituted by disk substrates having different thicknesses. In such anapparatus, one of parallel flat plates having different thicknesses isinserted in the optical path between an optical disk and the objectivelens depending on the thickness of the optical disk subjected toreproduction processing in such a manner that the sum of the opticalthickness of the parallel flat plate and that of the optical diskbecomes equal to the design lens load of the objective lens. With thisoperation, data can be stably reproduced from the optical disk while thetransmission wavefront aberration is always kept small.

In an apparatus using such a parallel flat plate, it is important that aparallel flat plate is inserted in the optical path without tilting theplate with respect to the optical disk and the objective lens. That is,a high precision is required for a moving mechanism for each parallelflat plate. In addition, if a parallel flat plate tilts with respect tothe objective lens, a coma is caused. Even if, therefore, the sphericalaberration is reduced by the insertion of the parallel flat plate, theshape of a focused spot is not improved. Furthermore, since the space(working distance) between the objective lens and an optical disk issmall, it is very difficult to insert a parallel flat plate in thisspace.

In another apparatus proposed (Japanese Patent Disclosure (KOKAI) No.5-241095), a parallel flat plate is inserted between the objective lensand the light source for the same purpose as described above. In someother apparatuses proposed (e.g., Japanese Patent Disclosure (KOKAI)Nos. 5-54406, 5-205282, and 5-266511), a compensating lens is insertedbetween the objective lens and the light source to properly reproducedata from various types of optical disks constituted by disk substrateshaving different thicknesses. According to these proposals, when thethickness of an optical disk contradicts the design lens load of theobjective lens, a spherical aberration is caused, and a beam spotfocused on the recording surface of the optical disk increases in size.As a result, data cannot be accurately reproduced. For this reason, thewavefronts of a light beam incident on the objective lens are adjustedto prevent a spherical aberration so as to form a small beam spot,thereby realizing stable reproduction of data from the optical disk.

As a means for preventing a spherical aberration, a wavefront correctinglens like a concave lens is used in Japanese Patent Disclosure (KOKAI)No. 5-54406; a compensating lens made of, e.g., a liquid crystalmaterial, in Japanese Patent Disclosure (KOKAI) No. 5-205282; and acorrecting lens constituted by a plurality of lens elements havingvariable gaps, in Japanese Patent Disclosure (KOKAI) No. 5-266511.

In an optical disk apparatus, however, the objective lens moves in thedirection of the optical axis while following the warp of an opticaldisk. Therefore, in the method of adjusting the wavefronts of a lightbeam incident on the objective lens to cancel out the sphericalaberration, if the warp of the optical disk is large, a change in thecurvature of a light beam incident on the objective lens cannot beneglected. As a result, the spherical aberration cannot besatisfactorily canceled out.

In still another apparatus proposed (Japanese Patent Disclosure (KOKAI)No. 4-95224 corresponding to U.S. Pat. No. 5,235,581), a plurality ofoptical heads respectively corresponding to optical disks constituted bydisk substrates having different thicknesses are selectively used toproperly reproduce data recorded on each of these optical disks. Morespecifically, each optical head includes a semiconductor laser as alight source, an objective lens, and a photodetector. In addition, inorder to selectively use these optical heads, head moving mechanisms arearranged in correspondence with the respective optical heads to move aselected optical head along the radial direction of an optical disk.

However, with these optical heads and head moving mechanisms arranged incorrespondence with the thicknesses of disk substrates, the overallarrangement of the optical disk apparatus is very complicated and largein size, thus impairing the essential merit that data can be read fromoptical disks constituted by substrates having different thicknesses,i.e., based on different specifications, by using one optical diskapparatus.

On the other hand, as a means for stably reproducing data from aplurality of types of optical disks having different recordingdensities, an apparatus designed to variably change the focal length ofthe objective lens has been proposed (Japanese Patent Disclosure (KOKAI)No. 5-54414). This apparatus uses a liquid crystal lens designed tovariably change the focal length by electrically controlling thecurvature of the lens in which a liquid crystal is sealed. When thedensity of the data recorded on an optical disk is high, the focallength of the lens is shortened. With this operation, stablereproduction of data from optical disks having different recordingdensities is always performed. Since the aperture of the lens does notchange, the NA increases with a decrease in focal length, and a smallbeam spot can be formed on the recording surface of an optical disk.

This method may be practical under the condition that the NA of anobjective lens is relatively small. However, since an objective lenshaving a large NA (e.g., NA=0.45 for a CD; NA=0.55 for an LD) is used tofocus a small beam spot on an optical disk, it is very difficult tochange the surface shape of the liquid crystal lens into a shape havinga small transmission wavefront aberration.

As described above, since the conventional optical head has only oneobjective lens, the optical recording/reproducing apparatus cannotproperly cope with a case wherein a plurality of data recording mediabased on different specifications associated with, e.g., recordingdensity, allowable warp amount, and substrate thickness, are to be used,or a case wherein different specifications are set for optimal lenses ina recording operation and a reproducing operation, respectively, withrespect to the same data recording medium.

Note that a plurality of special pickups (optical heads) using specialobjective lenses complying with the respective standards andspecifications may be prepared to be selectively used. In this case,however, the apparatus undergoes an increase in cost as well as anincrease in size. Therefore, this arrangement cannot be practical.

All the conventional methods known as techniques of properly reproducingdata recorded on a plurality of type of optical disks constituted bydisk substrates having different thicknesses by using one optical diskapparatus pose practical problems.

More specifically, in the method of inserting a parallel flat platebetween an optical disk and an objective lens, since the parallel flatplate is inserted in an optical path so as not to tilt with respect tothe optical disk and the objective lens, a high precision is requiredfor a moving mechanism for the parallel flat plate. If the parallel flatplate tilts with respect to the optical disk and the objective lens, acoma is caused to degrade the shape of a focused spot. In addition, itis very difficult to insert the parallel flat plate in the space betweenthe objective lens and the optical disk.

In the method of inserting a parallel flat plate or a compensating lensbetween an objective lens and a light source to adjust the wavefronts ofa light beam incident on the objective lens so as to prevent a sphericalaberration, since the objective lens moves in the direction of theoptical axis while following the warp of an optical disk, a change inthe curvature of a light beam incident on the objective lens cannot beneglected if the warp of the optical disk is large. For this reason, thespherical aberration cannot be satisfactorily canceled out.

Consider the apparatus in which a plurality of optical heads, eachhaving a semiconductor laser, an objective lens, and a photodetector,are arranged in correspondence with optical disks constituted bysubstrates having different thicknesses, and each optical head is movedalong the radial direction of an optical disk by a corresponding specialhead moving mechanism to be selectively used. Since this apparatusrequires a plurality of optical heads and head moving mechanisms equalin number thereto, the overall arrangement of the apparatus iscomplicated and large.

In the apparatus using a variable focus lens, e.g., a liquid crystallens designed to variably change the focal length by electrical control,to stably reproduce data from a plurality of types of optical diskshaving different recording densities, when an objective lens having alarge NA is used to form a small beam spot, it is very difficult tochange the surface shape of the liquid crystal lens into a shape havinga small spherical wavefront aberration.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical head for an optical data recording/reproducing apparatus, whichhas a small size and an inexpensive arrangement but performs a properrecording/reproducing operation with respect to a plurality of datarecording media demanding different specifications for objective lenses.

A related object of the present invention is to provide an optical headfor an optical data recording/reproducing apparatus, which has a smallsize and an inexpensive arrangement but performs proper recording andreproducing operations even if different specifications are set forobjective lenses in a recording operation and a reproducing operation,respectively.

According to the present invention, there is provided an optical headapparatus used for an optical data recording/reproducing device,comprising objective lenses for irradiating light onto a recordingmedium; and means for selecting a desired objective lens from theobjective lenses.

According to the present invention, there is provided another opticalhead apparatus comprising a movable member driven in a direction ofthickness of a recording medium and a direction perpendicular to thedirection of thickness, the movable member having a light source;objective lenses, mounted on the movable member, for irradiating lightfrom the light source onto the recording medium; and means for selectinga desired objective lens in accordance with a type of the recordingmedium, and locating the desired objective lens in an optical path ofthe light.

According to the present invention, there is provided a further opticalhead apparatus comprising

a movable member driven in a direction of thickness of a recordingmedium and a direction perpendicular to the direction of thickness, themovable member having a magnet; objective lenses, mounted on the movablemember, for irradiating light from the light source onto the recordingmedium; coil means, arranged around the movable member, for driving themovable member at least in the direction perpendicular the direction ofthickness; and means for selecting a desired objective lens inaccordance with a type of the recording medium, and locating the desiredobjective lens in an optical path of the light.

According to the present invention, there is provided a still anotheroptical head apparatus comprising a stationary optical system includinga light source for emitting light and a detection system for detectinglight reflected by a recording medium, and arranged at a position fixedto the recording medium; objective lenses for focusing/irradiating lightemitted from the light source onto the recording medium; a movablesupport member supporting the objective lenses and arranged to bemovable in a direction parallel to the recording medium; and controlmeans for controlling the movable support member to selectively locate adesired one of the objective lenses on an optical axis of the lightirradiated onto the recording medium.

Additional objects and advantages of the present invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present invention.The objects and advantages of the present invention may be realized andobtained by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe present invention and, together with the general description givenabove and the detailed description of the preferred embodiments givenbelow, serve to explain the principles of the present invention inwhich:

FIGS. 1A and 1B are graphs showing the relationship between thewavefront aberration and the degree of tilting of disk for thesubstrates with a different thickness;

FIG. 2 is a perspective view schematically showing the overallarrangement of an optical disk recording/reproducing apparatus includingan optical head according to the first embodiment of the presentinvention;

FIG. 3 is a block diagram showing a control system and an optical systemfor the recording/reproducing apparatus in FIG. 2;

FIG. 4 is a partially sectional side view schematically showing thearrangement of the optical head according to the first embodiment of thepresent invention;

FIG. 5 is a schematic view showing the basic arrangement of the opticaldisk recording/reproducing apparatus in FIG. 2;

FIG. 6 is a view showing a state wherein the first objective lens isselected in the first embodiment;

FIG. 7 is a view showing a state wherein the second objective lens isselected in the first embodiment;

FIG. 8 is a schematic view showing the overall basic arrangement of anoptical disk recording/reproducing apparatus including an optical headaccording to the second embodiment of the present invention;

FIG. 9 is a view showing a state wherein the first objective lens isselected in the second embodiment;

FIG. 10 is a view showing a state wherein the second objective lens isselected in the second embodiment;

FIG. 11 is a schematic perspective view showing the arrangement of themain part of an optical disk recording/reproducing apparatus includingan optical head according to the third embodiment of the presentinvention;

FIG. 12 is a view showing a state wherein the first objective lens isselected in the third embodiment;

FIG. 13 is a view showing a state wherein the second objective lens isselected in the third embodiment;

FIG. 14 is a schematic view showing a state wherein a plurality ofobjective lenses in the first to third embodiments are mounted;

FIG. 15 is a plan view schematically showing an overall optical diskrecording/reproducing apparatus including an optical head according tothe fourth embodiment of the present invention;

FIG. 16 is a sectional view taken along a line A-A' in FIG. 15, showntogether with an optical system;

FIG. 17 is a sectional view taken along a line B--B in FIG. 15;

FIG. 18 is a block diagram showing an optical system and a signalprocessing system according to the fourth embodiment of the presentinvention;

FIG. 19 is a plan view showing a movable portion of an optical headaccording to the fifth embodiment of the present invention;

FIG. 20 is a plan view showing a movable portion of an optical headaccording to the sixth embodiment of the present invention;

FIG. 21A is a plan view showing a movable portion of an optical headaccording to the seventh embodiment of the present invention;

FIG. 21B is a perspective view of the movable portion in the seventhembodiment;

FIG. 22 is a plan view showing a movable portion of an optical headaccording to the eighth embodiment of the present invention;

FIG. 23 is a plan view showing a movable portion of an optical headaccording to the ninth embodiment of the present invention;

FIG. 24 is a plan view showing a movable portion of an optical headaccording to the tenth embodiment of the present invention;

FIG. 25 is a sectional view of the tenth embodiment;

FIG. 26 is a plan view showing a movable portion of an optical headaccording to the eleventh embodiment of the present invention;

FIG. 27 is a plan view showing a movable portion of an optical headaccording to the twelfth embodiment of the present invention;

FIGS. 28A to 28F are plan views, each showing an example of using onecounterweight instead of an objective lens in the fourth to twelfthembodiments;

FIGS. 29A to 29C are plan views, each showing an example of using twocounterweights instead of an objective lens in the fourth to twelfthembodiments;

FIGS. 30A and 30B are plan views, each showing an example of using aflexible print board in the modification shown in FIG. 28B;

FIGS. 31A and 31B are plan views, each showing an example of using aflexible print board in the modification shown in FIG. 29B;

FIG. 32 is a plan view of a movable portion of an optical head accordingto the thirteenth embodiment of the present invention;

FIG. 33 is a sectional view taken along a line A-A' in FIG. 32;

FIG. 34 is a sectional view taken along a line B-B' in FIG. 32;

FIG. 35 is a sectional view taken along a line C-C' in FIG. 32;

FIG. 36 is a plan view of a movable portion of an optical head accordingto the fourteenth embodiment of the present invention;

FIG. 37 is a sectional view taken along a line A-A' in FIG. 36;

FIG. 38 is a partially sectional view taken along a line B-B' in FIG.37;

FIG. 39 is a sectional view taken along a line C-C' in FIG. 36;

FIG. 40 is a sectional view of a movable portion of an optical headaccording to the fifteenth embodiment of the present invention;

FIG. 41 is a plan view showing an operation state of the fifteenthembodiment;

FIG. 42 is another plan view showing an operation state of the fifteenthembodiment;

FIG. 43 is a plan view showing an operation state of an optical headaccording to the sixteenth embodiment of the present invention;

FIG. 44 is a plan view showing an operation state of the sixteenthembodiment;

FIG. 45 is a view showing the arrangement of the main part of an opticalhead according to the seventeenth embodiment of the present invention;

FIGS. 46A and 46B are views showing objective lenses and optical disksbased on different specifications for comparison;

FIGS. 47A and 47B are sectional views showing the typical sectionalshapes of objective lenses made of different nitrate materials;

FIG. 48 is a view showing the detail arrangement of a lens actuator inthe seventeenth embodiment;

FIG. 49 is view showing the shape of a tracking coil arranged on arotating blade in the seventeenth embodiment;

FIG. 50 is a view showing the more detailed arrangement of the lensactuator in the seventeenth embodiment;

FIG. 51 is a timing chart showing the waveforms of currents, eachsupplied to the tracking coil to select one of a plurality of objectivelenses arranged on the rotating blade in the seventeenth embodiment;

FIG. 52 is a view showing the arrangement of the main part of an opticalhead according to the eighteenth embodiment of the present invention;

FIG. 53 is a perspective view showing the arrangement of the main partof an optical head according to the nineteenth embodiment of the presentinvention;

FIG. 54 is a perspective view showing the arrangement of the main partof an optical head according to the twentieth embodiment of the presentinvention;

FIG. 55 is a perspective view showing the arrangement of the main partof an optical head according to the 21st embodiment of the presentinvention;

FIG. 56 is a view showing a correlation in the first specificationsbetween two objective lenses in the seventeenth to 21st embodiments;

FIG. 57 is a view showing a correlation in the second specificationsbetween two objective lenses in the seventeenth to 21st embodiments;

FIG. 58 is a view for explaining an adjustment method for the opticalhead apparatuses according to the seventeenth to 21st embodiments; and

FIG. 59 is a graph showing the relationship between the wavefrontaberration and the degree of tilting of the disk.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of an optical head according to the presentinvention will now be described with reference to the accompanyingdrawings.

First Embodiment!

The first embodiment will be described below with reference to FIGS. 2to 7.

The arrangement of the main part of an optical disk apparatus 1 as adata recording/reproducing apparatus according to the present inventionwill be described first with reference to FIGS. 2 to 4.

The optical disk apparatus 1 has a spindle motor 12 (see FIG. 3) as adisk driving means for holding and rotating/driving an optical disk 10(only a portion of which is indicated by the chain double-dashed line)as a data recording medium.

A pickup 20 as an optical head capable of linearly moving in the radialdirection (indicated by an arrow A) of the optical disk 10 is arrangedon the lower surface side of the optical disk 10 rotated by the spindlemotor 12. A movable optical system 18 constituted by a plurality ofdifferent types of (two, i.e., the first and second objective lenses inthis case) objective lenses 14a and 14b (to be described later), areflecting mirror 16 (see FIG. 4) as a laser beam guide means, and thelike is mounted on the pickup 20.

As shown in FIG. 2, a stationary optical unit 22 is arranged on theextended line of the path of the pickup 20 in the radial direction ofthe optical disk 10. The stationary optical unit 22 serves toirradiate/receive a laser beam LB onto/from the movable optical system18 mounted on the pickup 20.

The laser beam LB irradiated from the stationary optical unit 22 towardthe pickup 20 along the moving direction of the pickup 20 is reflectedat a right angle by the reflecting mirror 16 constituting the movableoptical system 18 and focused on a data recording surface 10a of theoptical disk 10 via the objective lens 14a (or 14b). The laser beam LBreflected by the data recording surface 10a passes through the objectivelens 14a (or 14b) and is deflected horizontally by the reflecting mirror16 to be guided to the stationary optical unit 22, thereby performingdata read processing.

As shown in FIG. 3, the stationary optical unit 22 includes asemiconductor laser 24 as a laser beam generating means for generatingthe laser beam LB, a collimator lens 26 for collimating the laser beamLB generated by the semiconductor laser 24, a first beam splitter 28 forsplitting the laser beam LB into a laser beam LB propagating to theoptical disk 10 and a reflected laser beam reflected by the optical disk10, a second beam splitter 30 for splitting the reflected laser beam LBreflected by the optical disk 10 into a first beam used for focuscontrol and data reproduction and a second beam used for trackingcontrol, first and second focusing lenses 32 and 34 for respectivelyfocusing the first and second beams, first and second photodetectors 36and 38 for respectively converting the first and second beams intoelectrical signals, and the like.

The stationary optical unit 22 having the above arrangement is connectedto a control section 42 as a control means via a signal cable 40 (seeFIG. 2). The control section 42 includes a data write circuit 44 forgenerating a recording signal in accordance with data input from anexternal host system (not shown), e.g., a host computer system, anobjective lens selector 48 for generating a switching signal to anobjective lens selecting means 46 (to be described later) in accordancewith the data input from the host computer system, a data read circuit50 for reproducing data recorded on the optical disk 10 from a detectionsignal detected via the stationary optical unit 22, a trackingcontroller 52 for generating a tracking control signal for controllingtracking of the objective lens 14a (or 14b), a focus controller 54 forgenerating a focus control signal for performing focus control of theobjective lens 14a (or 14b), and the like.

The laser beam LB irradiated from the semiconductor laser 24 isconverted into a parallel beam via the collimator lens 26, deflected at90° by the first beam splitter 28, and incident on the movable opticalsystem 18 of the pickup 20. That is, the laser beam LB is incident onthe objective lens 14a (or 14b), selected in the manner described later,via the reflecting mirror 16. The laser beam LB incident on theobjective lens 14a (or 14b) undergoes a converging effect via theobjective lens 14a (or 14b) and is focused on the data recording surface10a of the optical disk 10 to form a beam spot.

When the optical disk apparatus 1 is in the reproduction mode, the laserbeam LB guided onto the optical disk 10 is intensity-modulated inaccordance with data recorded on the data recording surface 10a, i.e.,the presence/absence of very small pits 56. The resultant beam isreturned to the objective lens 14a (or 14b) again.

The laser beam LB returned to the objective lens 14a (or 14b) is guidedto the stationary optical unit 22 via the reflecting mirror 16,transmitted through the first beam splitter 28, and split into two beamsby the second beam splitter 30. The beams are respectively focused onthe first and second photodetectors 36 and 38 via the first focusinglenses 32 and 34.

The laser beams LB guided to the first photodetectors 36 and 38 arerespectively converted into electrical signals. The electrical signalsare respectively supplied to the tracking controller 52 and the focuscontroller 54 to be used for focus control and tracking control of theobjective lens 14a (or 14b). Note that the laser beam LB guided to thesecond photodetector 38 is also supplied to the data read circuit 50 toreproduce data recorded on the optical disk 10. The reproduction resultis output to a host computer (not shown).

In this case, the pickup 20 is controlled/moved (tracking control) inthe radial direction of the optical disk 10 in accordance with a trackposition on the data recording surface 10a of the optical disk 10 atwhich a beam spot is to be irradiated.

The arrangement of the pickup 20 as an optical head will be describednext with reference to FIGS. 3 and 4.

The pickup 20 has a carriage 60 as a moving means capable of moving inthe radial direction (indicated by the arrow A) of the optical disk 10,i.e., the tracking control direction, by using a linear motor 74 (to bedescribed later) as a drive source.

A plurality of (two in this case) pairs of support rollers 62 arearranged, as roller pairs each supported through a leaf spring, on thetwo side portions of the carriage 60. As shown in FIG. 2, these supportrollers 62 are brought into rolling contact with two guide shafts 64arranged horizontally and parallelly along the radial direction of theoptical disk 10 so as to be movably supported in the radial direction(indicated by the arrow A).

In addition, radial coils 66 are mounted on the two side portions of thecarriage 60. These radial coils 66 are fitted on inner yokes 68 asmembers constituting a magnetic circuit. The inner yokes 68 areconnected to outer yokes 70. Magnets 72 are mounted on the inner sidesof the outer yokes 70, thereby constituting the linear motor 74.

When power is supplied to the radial coils 66, a thrust (Lorentz force)is generated to reciprocate the carriage 60 in the tracking controldirection.

FIG. 4 is a sectional view of the main part of the carriage 60. As shownin FIG. 4, a support shaft 80 as a rotational center axis extendsvertically from the upper surface of the carriage 60. The support shaft80 is parallel to the rotational center axis of the optical disk 10,i.e., the driving shaft 12a (see FIG. 3) of the spindle motor 12.

A lens actuator 82 as a lens holding member is mounted on the supportshaft 80, with a rotational center hole 82a being fitted on the supportshaft 80, so as to be rotatable in the direction indicated by an arrow Band movable in the vertical direction (indicated by an arrow C).

The lens actuator 82 has a columnar shape, with a lens mount flangeportion 84 being formed on the upper end side. The rotational centerhole 82a vertically extends through the central portion of the lensactuator 82.

The first and second objective lenses 14a and 14b suitable for differenttypes of optical disks 10 are arranged on the lens mount flange portion84 to be symmetrical about the support shaft 80 as the rotational centeraxis of the lens actuator 82. By selectively rotating the lens actuator82 in the direction indicated by the arrow B, the first and secondobjective lenses 14a and 14b can be selectively inserted in the opticalpath of the laser beam LB.

Ring-like magnets 86 and 88 are respectively mounted on the lowersurface of the lens actuator 82 and the upper surface of the carriage 60so as to magnetically repel each other. In this embodiment, the opposingsurfaces of the two magnets have the N poles. With this arrangement, theweight of the lens actuator 82 is canceled out to be rotated andvertically moved with a small force.

A focusing coil 90 is wound on a vertically intermediate portion of thelens actuator 82. A focusing magnet 92 corresponding to the focusingcoil 90 is fixed to the carriage 60 via a holding member (not shown). Bysupplying a current to the focusing coil 90, the lens actuator 82 can bemoved in the focus control direction (indicated by the arrow C) tofollow vertical vibrations caused by, e.g., the warp of the optical disk10.

A rack 94 is formed on the lower end portion of the lens actuator 82. Apinion 96 is meshed with the rack 94. The pinion 96 is mounted on thedriving shaft of a motor 98 mounted on the carriage 60 and capable ofrotating clockwise and counterclockwise. By driving the motor 98, thelens actuator 82 can be selectively rotated in the direction indicatedby the arrow B or in the direction reverse thereto. These componentsconstitute a lens actuator moving means 100 as a lens holding membermoving means.

With the lens actuator moving means 100, the first or second objectivelens 14a or 14b can be selectively inserted in the optical path of thelaser beam LB, and the objective lens 14a or 14b can also be moved inthe direction indicated by an arrow D (see FIG. 5), which isperpendicular to a recording pit 56 array on the optical disk 10 tofollow the pit 56 array on the optical disk 10, thereby moving theobjective lens 14a or 14b in the radial direction to follow a largetracking error.

The objective lenses 14a and 14b are mounted on the lens mount flangeportion 84 via tracking control mechanisms 110 respectively havingtracking coils 112 (see FIG. 3) so as to follow a small tracking error.

The lens actuator 82 serving as a lens holding member and the lensactuator moving means 100 having the above arrangement constitute theobjective lens selecting means 46 for selectively inserting the first orsecond objective lens 14a or 14b in the optical path of the laser beamLB. Cables (not shown) for supplying power are respectively connected tothe focusing coil 90, a tracking coil (not shown), and the motor 98 ofthe lens actuator moving means 100.

FIG. 5 schematically shows the basic arrangement of the optical diskapparatus 1 as the data recording/reproducing apparatus according to thepresent invention described above. Note that an arrow E indicates therotating direction of the optical disk 10.

The first and second objective lenses 14a and 14b are suitable forrecording/reproducing operations with respect to a plurality of (two inthis embodiment) optical disks 10a and 10b based on different standardsassociated with, e.g., recording density, allowable warp amount, andsubstrate thickness.

Assume that the optical disk 10 is the optical disk 10a having a thicksubstrate 102. In this case, the first objective lens 14a suitable forthe optical disk 10a is selected by a signal from the control section 42to be inserted in the optical path of the laser beam LB, as shown inFIG. 6. Assume that optical disk 10 is the disk 10b having a thinsubstrate 102. In this case, the second objective lens 14b suitable forthis disk is selected and inserted in the optical path of the laser beamLB, as shown in FIG. 7.

In the above description, the first and second objective lenses 14a and14b are suitable for processing a plurality of (two in this embodiment)optical disks 10a and 10b based on different standards associated with,e.g., recording density, allowable warp value, and substrate thickness.However, the present invention is not limited to this. If differentspecifications are set for objective lenses in a recording operation anda reproducing operation, respectively, with respect to the same opticaldisk 10, the first and second objective lenses 14a and 14b may beselectively used for a recording operation and a reproducing operation,respectively.

In the above description, the optical head has two objective lenses.However, the present invention is not limited to this and may be appliedto an arrangement having three or more objective lenses which are to beswitched. That is, the present invention is effective for an arrangementhaving a plurality of objective lenses which are to be switched.

According to the first embodiment, since a predetermined objective lenscan be selected (and used) from a plurality of objective lenses suitablefor the respective types of data recording media, in which signals to beread out are stored, in accordance with the type of a data recordingmedium, proper data processing can be performed with respect to aplurality of data recording media requiring different specifications forobjective lenses with a small, inexpensive arrangement.

More specifically, one of the plurality of objective lenses 14a and 14bwhich is suitable for a recording/reproduction operation with respect toan optical disk is selected by changing the pivot angle of the lensactuator 82, instead of preparing a plurality of special pickups usingspecial objective lenses suitable for the respective standards andspecifications, and selectively using the pickups in accordance with thecharacteristics of an optical disk. Therefore, with a small, inexpensivearrangement, proper recording/reproducing operations can be performedwith respect to the plurality of optical disks 10a and 10b requiringdifferent specifications for the objective lenses 14a and 14b.

Since the objective lenses 14a and 14b are arranged to be symmetricalabout the support shaft 80 as the rotational center axis of the lensactuator 82, the masses of the two objective lenses 14a and 14b balanceeach other to allow easy balancing of the lens actuator 82. In addition,since the objective lenses 14a and 14b are switched by using the lensactuator 82, this switching operation is easy to perform.

Other embodiments of the present invention will be described next. Thesame reference numerals in the first embodiment denote the same parts asin the following embodiments, and a detailed description thereof will beomitted.

Second Embodiment!

The second embodiment of the present invention will be described belowwith reference to FIGS. 8 to 10. Note that the same reference numeralsin the first embodiment denote the same parts as in the secondembodiment, and a repetitive description will be avoided.

FIG. 8 schematically shows the basic arrangement of the secondembodiment. Each of FIGS. 9 and 10 shows a state where objective lenses14a and 14b are switched in accordance with the type of an optical disk(optical disk 10a or 10b).

As is apparent from these drawings, unlike in the first embodiment, inthe second embodiment, the objective lenses 14a and 14b are arranged atadjacent positions instead of being arranged to be symmetrical about therotating shaft. In addition, the second embodiment includes an objectivelens selecting means 460 for switching the objective lenses 14a and 14bby using a tracking mechanism 115 constituted by a tracking coil 45 anda magnet 47, which are mounted on a lens actuator 82 without using anyrack and pinion, and designed to move each objective lens in thedirection indicated by an arrow D, which is perpendicular to a recordingpit 56 array on an optical disk 10, so as to cause the objective lens tofollow a tracking error.

As described above, similar to the first embodiment, in the secondembodiment, proper recording/reproducing operations can be performedwith respect to the plurality of optical disks 10a and 10b requiringdifferent specifications for the objective lenses 14a and 14b.Furthermore, since the plurality of objective lenses 14a and 14b arelocated at adjacent positions, the objective lenses can be easilyswitched within a short period of time.

In addition, the objective lenses 14a and 14b are switched by using thelens actuator 82, and the tracking mechanism 115 can be used as aselecting means for the objective lenses 14a and 14b. Therefore, themechanism can be simplified.

Note that in the second embodiment, the first and second objectivelenses 14a and 14b are applied to processing of the plurality of opticaldisks 10a and 10b based on different standards associated with, e.g.,recording density, allowable warp amount, and substrate thickness,similar to the first embodiment. However, the present invention is notlimited this. For example, it is apparent that when differentspecifications are set for objective lenses in a recording operation anda reproducing operation with respect to one optical disk 10, the firstand second objective lenses 14a and 14b may be selectively used for arecording operation and a reproducing operation, respectively.

Further, the present invention is not limited to the optical head havingtwo objective lenses, but may be applied to the optical head havingthree or more objective lenses.

Third Embodiment!

The third embodiment of the present invention will be described belowwith reference to FIGS. 11 to 13. Note that the same reference numeralsin the third embodiment denote the same parts as in the firstembodiment, and a repetitive description will be avoided.

The third embodiment includes a pickup 200 as an optical head having anarm type lens actuator 820 in place of the rotary type lens actuator 82described above.

The lens actuator 820 is constituted by a support member 120 capable ofpivoting on a support shaft 800, as a rotational center axis, whichextends vertically from a carriage 60, only in the direction indicatedby an arrow G (see FIGS. 12 and 13), a lens holder 121 as a lens holdingmember for holding objective lenses 14a and 14b, and a parallel leafspring 122 for coupling the lens holder 121 to the support member 120and supporting the lens holder 121 to allow it to move in the focuscontrol direction.

If, for example, an optical disk is an optical disk 10a constituted by athick substrate 102, the first objective lens 14a suitable for thisoptical disk can be selected and inserted in the optical path of a laserbeam LB by pivoting the lens actuator 820 on the support shaft 800 asthe rotational center axis by using an objective lens selecting means460, as shown in FIG. 12. If the optical disk 10 is an optical disk 10bconstituted by a thin substrate 102, control is performed to select thesecond objective lens 14b suitable for this optical disk and insert itin the optical path of the laser beam LB, as shown in FIG. 13.

The objective lens selecting means 460 is constituted by a magnet 124mounted on the support member 120, an electromagnet 126 arranged nearthe magnet 124, and a polarity switching means 128 for switching thepolarities of the two poles of the electromagnet 126 in accordance withthe direction in which a current flows.

According to the third embodiment, the first and second objective lenses14a and 14b are applied to processing of the plurality of optical disks10a and 10b based on different standards associated with, e.g.,recording density, allowable warp amount, and substrate thickness,similar to the first embodiment. However, the present invention is notlimited this. For example, it is apparent that when differentspecifications are set for objective lenses in a recording operation anda reproducing operation with respect to one optical disk 10, the firstand second objective lenses 14a and 14b may be selectively used for arecording operation and a reproducing operation, respectively.

Further, the present invention is not limited to the optical head havingtwo objective lenses, but may be applied to the optical head havingthree or more objective lenses.

FIG. 14 schematically shows a state wherein the first and secondobjective lenses 14a and 14b are mounted in the first to thirdembodiments. The focal lengths of the objective lenses 14a and 14b areset such that the distances between the first and second objectivelenses 14a and 14b and the optical disks 10a and 10b, i.e., workingdistances H, become constant.

Assume that the objective lens 14a having a numerical aperture (NA) of0.45 is used for the optical disk 10a for a CD, which is constituted bythe substrate 102 having a thickness T₁ of 1.2 mm; and the objectivelens 14b having an NA of 0.6, for the optical disk 10b constituted bythe substrate 102 having a thickness T₂ of 0.6 mm. In this case, thefocal length of the objective lens 14a is set to be f=2.8 mm, and thefocal length of the objective lens 14b is set to be f=2.4 mm.

If the focal lengths are set to make the working distances H constant,servo control can be easily performed. At the same time, this serves toprevent accidents such as collision between the optical disks 10a and10b and the objective lenses 14a and 14b. Such settings are veryimportant for practical design.

Referring to FIG. 14, reference numeral 103 denotes a data recordinglayer with a tracking guide which is formed on a data recording surface.

Fourth Embodiment!

An objective lens driving unit according to the fourth embodiment of thepresent invention will be described below with reference to FIGS. 15 to18. FIG. 15 is a plan view showing the objective lens driving unit. FIG.16 is a sectional view taken along a line A-A' of the objective lensdriving unit in FIG. 15, together with an optical processing system.FIG. 17 is a sectional view taken along a line B-B' of the objectivelens driving unit in FIG. 15. FIG. 18 is a view showing an opticalsystem and a signal processing system.

A disk 101 (e.g., an optical disk or a magnetooptical disk) used for adata recording/reproducing operation is held by a chucking means such asa magnetic chuck with respect to a spindle motor 103 fixed to a base102. The disk 101 is stably rotated/driven by the spindle motor 103 in arecording/reproducing operation.

A movable member 104 is arranged below the disk 101 at a position nearthereto. The movable member 104 is constituted by first and secondmovable members 105 and 106 and supported to be movable in the radialdirection and direction of thickness of the disk 101.

The first movable member 105 is constituted by a flat blade 105a havinga substantially elliptic shape and opposing the disk 101 surface, and acylindrical coil bobbin 105b fixed to the lower portion of the blade105a. A slide bearing 105c is arranged in the center of the blade 105aand the coil bobbin 105b.

A rotating shaft 107 having one end fixed to the second movable member106 to extend vertically therefrom is inserted in the slide bearing 105cwith a small gap (10 micron or less). The first movable member 105 canbe rotated about the rotating shaft 107 and translated in the axialdirection thereof.

A plurality of (two in this case) objective lenses 108a and 108b arefixed on the blade 105a to be spaced apart from each other. As theseobjective lenses 108a and 108b, objective lenses having differentoptical characteristics (e.g., the numerical aperture (NA) of theobjective lens 108a is 0.45, and the NA of the objective lens 108b is0.6) are selected. These two objective lenses 108a and 108b are arrangedon a diameter passing through the rotating shaft 107 at an equaldistance from the center axis such that the center of gravity of thetotal mass of the first movable member 105 almost coincides with therotating shaft 107. That is, the structure of the first movable member105 achieves a good balance in weight with respect to the rotating shaft107 owing to the two objective lenses 108a and 108b.

A focus coil 109 is wound around the coil bobbin 105b. Two rectangulartracking coils 200a and 200b, each of which is two-dimensionally wound,are bonded to the focus coil 109 to be spaced apart from each other by apredetermined distance. Magnetic circuits 112a and 112b respectivelyconstituted by permanent magnets 110a and 110b and the yokes 111a and111b are arranged around the focus coil 109 and the tracking coils 200aand 200b and above the second movable member 106 to be symmetrical aboutthe rotating shaft 107. The magnetic circuits 112a and 112b are arrangedto oppose the focus coil 109 and the tracking coils 200a and 200b viamagnetic gaps, each having a predetermined length so as to providemagnetic fields for the focus coil 109 and the tracking coils 200a and200b. Note that the two magnetic circuits 112a and 112b have the samestructure, and the directions of magnetization of the permanent magnets110a and 110b coincide with the directions of thickness of the magneticgaps, respectively.

When the focus coil 109 is energized, it receives magnetic fluxes fromthe magnetic circuits 112a and 112b to generate a Lorentz force. As aresult, the first movable member 105 is slightly translated in thedirection of thickness (the axial direction of the rotating shaft 107)of the disk 101. When the tracking coils 200a and 200b are energized,they receive magnetic flexes from the magnetic circuits 112a and 112b togenerate a Lorentz force. As a result, the first movable member 105 isslightly rotated/driven in the radial direction (about the rotatingshaft 107) of the disk 101.

Two magnetic members 201a and 201b consisting of iron pieces or the likeare arranged on the tracking coils 200a and 200b at positions spacedapart from each other by 180° around the coil bobbin 105b. The magneticmembers 201a and 201b are bonded to the tracking coils 200a and 200b atpositions spaced apart from the two objective lenses 108a and 108b by90° to be symmetrical about the rotating shaft 107. When one objectivelens 108a (or 108b) is in an optical path 124 (to be described later),these magnetic members 201a and 201b are arranged to oppose the magneticgaps of the magnetic circuits 112a and 112b.

As described above, the second movable member 106 is connected to thefirst movable member 105 via the rotating shaft 107. A pair of radialcoils 113a and 113b are mounted on the two end portions of the secondmovable member 106 at an equal distance from the center-of-gravityposition of the second movable member 106. The radial coils 113a and113b receive magnetic fields from radial magnetic circuits 114a and 114bfixed to the base 102.

The radial magnetic circuits 114a and 114b are respectively constitutedby back yokes 115a and 115b, center yokes 116a and 116b, and permanentmagnets 117a and 117b. The radial coils 113a and 113b movably extendthrough in magnetic gaps defined by the center yokes 116a and 116b andthe permanent magnets 117a and 117b. Note that the two radial magneticcircuits 114a and 114b have the same structure, and the directions ofmagnetization of the permanent magnets 117a and 117b coincide with thedirections of thickness of the magnetic gaps.

Two pairs of slide bearings 119a and 119b, i.e., four slide bearings,are respectively arranged on the left and right sides of the secondmovable member 106.

Two guide rails 118a and 118b are arranged to be parallel to each otherto extend through these slide bearings. Note that the two ends of eachof the guide rails 118a and 118b are fixed to the base 102. The secondmovable member 106 is supported to be movable along the guide rails 118aand 118b.

When the radial coils 113a and 113b are energized, they receive magneticfluxes from the radial magnetic circuits 114a and 114b to generate aLorentz force. As a result, the second movable member 106 is translatedin the radial direction of the disk 101.

The widths of the magnetic gaps defined by the radial magnetic circuits114a and 114b are set to be sufficiently large in the same directionsuch that the second movable member 106 can be moved by a requireddistance in the longitudinal direction of the guide rails 118a and 118b,i.e., the objective lenses 108a and 108b can be moved in the radialdirection from the outermost periphery to the innermost periphery of thedisk 101.

The optical system and the signal processing system of the apparatuswill be described with reference to FIGS. 16 and 18. A laser beam to beirradiated on the disk 101 is generated by an optical unit 120 fixed tothe lower portion of the movable member 104 to be movable integrallywith the movable member 104. A laser beam LB irradiated from asemiconductor laser 121 in the optical unit 120 is collimated by acollimator lens 122. The parallel beam is then deflected at 90° by afirst beam splitter 123a and guided into the second movable member 106from the radial direction of the disk 101. An optical path (specificallya space) 141 is formed in the bottom portion of the second movablemember 106 to receive the laser beam LB. The laser beam LB passesthrough the optical path 141 and is incident on the objective lens 108a(or 108b). The laser beam LB incident on the objective lens 108a (or108b) undergoes a predetermined converging effect to be focused on thedata storage surface of the disk 101.

When the system is in the data reproduction mode, the laser beam LBguided to the disk 101 is intensity-modified in accordance with datarecorded on the data storage surface, i.e., the present/absence of smallpits, and is returned to the objective lens 108. The reflected laserbeam LB returned to the objective lens 108 passes through the opticalpath 141 again to be guided to the optical unit 120. The laser beam LBpasses through the first beam splitter 123a is split into two paths by asecond beam splitter 123b. The two resultant light beams arerespectively focused on first and second photodetectors 125a and 125bvia focusing lenses 124a and 124b.

The reflected laser beams LB guided to the photodetectors 125a and 125bare respectively converted into electrical signals and are supplied to atracking control circuit 127 and a focus control circuit 128 arranged ina control section 126. Signals generated by the tracking control circuit127 and focus control circuit 128 are used, as a focus offset signal anda tracking offset signal for the objective lens 108 (108a or 108b), forfocus direction control and tracking direction control.

The positional offset (focus offset) of the objective lens 108 in thefocus direction is detected by using the focus offset signal and atracking offset signal. The value of a current supplied to the focuscoil 109 is controlled such that this positional offset is corrected. Inaddition, the positional offset of the objective lens 108 in thetracking direction is detected by using the tracking offset signal. Thevalue of a current supplied to tracking coils 100a and 100b iscontrolled such that this positional offset is corrected.

The reflected laser beam LB guided to the photodetector 125b is alsosupplied to a data read circuit 129. The data represented by the laserbeam LB are various data recorded on the disk 101, which are supplied toa host system (e.g., a personal computer) (not shown) to be output ascharacters, a still picture, or a motion picture from a display or apiece of music or sounds from a loudspeaker. In this case, the secondmovable member 106 is controlled to move in the radial direction of thedisk 101 by a coarse or fine driving operation so as to follow tracks onthe data recording surface of the disk 101.

The control section 126 includes a data write circuit 130 for generatinga recording signal in accordance with data input from an external hostsystem (e.g., a personal computer) (not shown), and an objective lensselector 131 for generating a signal for rotating/controlling the firstmovable member 105 to set one of the objective lenses 108a and 108b inthe optical path 124 of the laser beam LB.

Switching of the two objective lenses 108a and 108b will be describednext.

The disk 101 which can be used in the apparatus of the present inventionis not limited to one type of disk as in the conventional apparatus, buta plurality of disks based on different standards associated with, e.g.,disk recording density, allowable warp amount, and disk substratethickness can be used. For example, not only a CD-ROM disk but also MOand PC disks and the like can be used. As the two objective lenses 108aand 108b, objective lenses suitable for processing of available disksare prepared.

If, for example, a disk requiring the laser beam LB to have a small spotdiameter is to be used, an objective lens having a large numericalaperture (NA) is selected. If a disk requiring the laser beam LB to havea large spot diameter is to be used, an objective lens having a small NAis selected.

When the user places the desired disk 101 on the spindle motor 103, dataindicating the type of the disk 101 (e.g., data indicating "CD-ROMdisk", "PC disk", or the like as data of the disk based on a differentstandard) is input through a host system (e.g., a personal computer).This input signal is supplied to the objective lens selector 131 toperform control to move the corresponding objective lens 108a (or 108b)onto the optical path 141 of the laser beam LB.

If the objective lens 108a (or 108b) corresponding to the placed disk101 has already been on the optical path 141, the first movable member105 need not be greatly moved. If, however, the required objective lens108a (or 108b) is spaced apart from the optical path 141 by 180° withrespect to the rotating shaft 107, a large current is instantaneouslysupplied to the tracking coils 200a and 200b.

The current supplied in this case has a current value required to guidethe first movable member 105 onto the optical path 141 with a largeacceleration within a short period of time, unlike a current for finedriving control of the first movable member 105.

When the first movable member 105 is rotated/accelerated to cause apredetermined objective lens 108a (or 108b) to reach the optical path141, the magnetic members 201a and 201b reach the positions where theyoppose the magnetic gaps defined by the magnetic circuits 112a and 112b.In this case, while the magnetic members 201a and 201b oppose themagnetic circuits 112a and 112b, the magnetic members 201a and 201breceive the maximum magnetic attraction forces from the magneticcircuits 112a and 112b. For this reason, if a large current isinstantaneously supplied to the tracking coils 200a and 200b, the firstmovable member 105 is reliably decelerated/stopped and positionedwithout supplying a special current for a decelerating/stoppingoperation, when the objective lens 108 reaches the optical path 124.

As described above, according to the fourth embodiment which is operatedin the above manner, since two objective lenses can be switched and usedin accordance with the standards or specifications of a disk, aplurality of objective lens driving units suitable for the standards orspecifications of a disk need not be prepared. Therefore, there isprovided an optical head which can properly handle various data withoutrequiring any other optical head.

In addition, since a plurality of magnetic circuits and magnetic membersare used, magnetic attraction forces acting on the first movable membercan be easily balanced. For this reason, the slide bearings 119a and119b are not pressed against the rotating shaft 107, and the frictionalforce, a so-called "rubbing", between the first movable member 105 andthe rotating shaft 107 can be minimized. This allows the first movablemember 105 to smoothly rotate and translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Fifth Embodiment!

An objective lens driving unit according to the fifth embodiment of thepresent invention will be described next with reference to FIG. 19. Notethat the same reference numerals in the fifth embodiment denote the sameparts as in each embodiment described above, and a repetitivedescription will be avoided.

A characteristic feature of this embodiment is that three objectivelenses are mounted on a first movable member. More specifically, a blade105a of a first movable member 105 is shaped to have three protrudingportions spaced apart from each other by 120° with respect to a rotatingshaft 107. Objective lenses 108a, 108b, and 108c are respectivelyfixed/arranged on these protruding portions. Three magnetic circuits112a, 112b, and 112c are fixed to a second movable member 106 to besymmetrical about the rotating shaft 107. The objective lenses 108a,108b, and 108c and the magnetic circuits 112a, 112b, and 112c arearranged at equal angular intervals on the same circumference around therotating shaft 107 as the center. Three tracking coils 200a, 200b, and200c and three magnetic members 201a, 201b, and 201c, each consisting ofan iron piece or the like, are bonded to a coil bobbin 105b at equalangular intervals. (Note that the magnetic members 201a, 201b, and 201care bonded in the state shown in FIG. 17).

As a basic structure for supporting the first movable member 105 toallow it to move in the focus direction and the radial direction, thesame slide bearing mechanism as that in the fourth embodiment isemployed. In addition, since the structure and operation of the secondmovable member 106 are the same as those in the fourth embodiment, anillustration and description thereof will be omitted.

According to the embodiment having such an arrangement, magnetic gapsfor providing magnetic fields for a focus coil 109 and the trackingcoils 200a, 200b, and 200c, which are equal in number to the objectivelenses 108a, 108b, and 108c are present and located at equal angularintervals on the same circumference around the rotating shaft 107 as thecenter. Since the magnetic members 201a, 201b, and 201c for determiningthe neutral position of the first movable member 105, equal in number tothe objective lenses 108a, 108b, and 108c, are mounted, a predeterminedone of the objective lenses 108a, 108b, and 108c can be reliablypositioned on an optical path 141 by the same control method as that inthe fourth embodiment.

In the optical head of this embodiment, since the three objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of special (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an optical head which canproperly handle various data without requiring any other optical heads.

Since pluralities of magnetic circuits and magnetic members are used,magnetic attraction forces acting on the first movable member can beeasily balanced. For this reason, the slide bearings are not pressedagainst the rotating shaft, and the frictional force, a so-called"rubbing", between the first movable member and the rotating shaft canbe minimized. This allows the first movable member to smoothly rotateand translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Sixth Embodiment!

Optical head according to the sixth embodiment of the present inventionwill be described next with reference to FIG. 20. A characteristicfeature of this embodiment is that four objective lenses are mounted ona first movable member. More specifically, a blade 105a of a firstmovable member 105 is shaped to have four protruding portions separatedfrom each other by 90° with respect to a rotating shaft 107. Objectivelenses 104a, 104b, 104c, and 104d are fixed/arranged on these protrudingportions. Four magnetic circuits 112a, 112b, 112c, and 112d are fixed toa second movable member 106 to be symmetrical about the rotating shaft107. The objective lenses 104a, 104b, 104c, and 104d and the magneticcircuits 112a, 112b, 112c, and 112d are arranged at equal angularintervals on the same circumference around the rotating shaft 107 as thecenter. In addition, four tracking coils 200a, 200b, 200c, and 200d andfour magnetic members 201a, 201b, 201c, and 201d, each consisting of aniron piece or the like, are bonded to a coil bobbin 105b at equalangular intervals. (Note that the magnetic members 201a, 201b, 201c, and201d are bonded in the state shown in FIG. 18.)

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

According to the embodiment having such an arrangement, magnetic gapsfor providing magnetic fields for a focus coil 109 and the trackingcoils 200a, 200b, 200c, and 200d, which are equal in number to theobjective lenses 108a, 108b, 108c, and 108d, are present and located atequal angular intervals on the same circumference around the rotatingshaft 107 as the center. Since the magnetic members 201a, 201b, 201c,and 201d for determining the neutral position of the first movablemember 105, which are equal in number to the objective lenses 108a,108b, 108c, and 108d, are mounted, a predetermined one of the objectivelenses 108a, 108b, 108c, and 108d can be reliably positioned on anoptical path 141 by the same control method as that in the fourthembodiment.

In the optical head of this embodiment, since the four objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of special (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an optical head which canproperly process various data without requiring any other objective lensdriving units.

Since pluralities of magnetic circuits and magnetic members are used,magnetic attraction forces acting on the first movable member can beeasily balanced. For this reason, the slide bearings are not pressedagainst the rotating shaft, and the frictional force, a so-called"rubbing", between the first movable member and the rotating shaft canbe minimized. This allows the first movable member to smoothly rotateand translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

The above three embodiments respectively exemplify the cases wherein thenumbers of objective lenses are set to be two, three, and four. However,the present invention is not limited to these numbers. The requiredeffects can be obtained by performing the same control as describedabove with a plurality of objective lenses.

The relationship between the numbers of objective lenses, magneticmembers, and magnetic gaps is preferably set such that the numbers ofmagnetic members and magnetic gaps are divisors of the number ofobjective lenses, for example: two magnetic gaps and six magneticmembers for six objective lenses; three magnetic gaps and six magneticmembers for six objective lenses; six magnetic gaps and six magneticmembers for six objective lenses; and two magnetic gaps and threemagnetic members for six objective lenses. Note that a plurality ofmagnetic members may be mounted at almost the same position to opposeone magnetic circuit.

By using such a combination, neutral positions determined by magneticattraction forces between magnetic members and magnetic gaps, which areequal in number to objective lenses, can be arranged. In addition, themagnetic attraction forces between the magnetic members and the magneticgaps cancel each other to further reduce the frictional force, i.e.,so-called "rubbing" between the first movable member and the rotatingshaft.

Seventh Embodiment!

An optical head according to the seventh embodiment of the presentinvention will be described next with reference FIGS. 21A and 21B. FIG.21A is a plan view of the seventh embodiment. FIG. 21B is a perspectiveview showing the arrangement of tracking coils and a focus coil.

A characteristic feature of this embodiment is that a first movablemember is different in shape from that in each embodiment describeabove. More specifically, a blade 105a as a part of a first movablemember 105 is circular, and the diameter of a coil bobbin 105b isslightly larger than that in each embodiment described above. Thediameter of the blade 105a is almost equal to that of the coil bobbin105b. The first movable member 105 has a cylindrical shape as a whole.

Consequently, magnetic circuits 112a and 112b opposing a focus coil 109and tracking coils 200a and 200b bonded to the coil bobbin 105b areformed to have larger curvatures than those in each embodiment describedabove.

Notches are formed in the first movable member 105, and magnetic members201a and 201b are embedded in the notches.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

In this embodiment having the above structure, the same effects asdescribed above can be obtained by performing the same operation as thatin each embodiment described above.

In the optical head of this embodiment, since the two objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of dedicated (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an optical head which canproperly process various data without requiring any other optical heads.

Since pluralities of magnetic circuits and magnetic members are used,magnetic attraction forces acting on the first movable member can beeasily balanced. For this reason, the slide bearings are not pressedagainst the rotating shaft, and the frictional force, a so-called"rubbing", between the first movable member and the rotating shaft canbe minimized. This allows the first movable member to smoothly rotateand translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase. Note that even if these objective lenses are arranged to besymmetrical about the rotating shaft or arranged around the rotatingshaft at equal intervals, the same effects as described above can beexpected.

Eighth Embodiment!

An optical head according to the eighth embodiment of the presentinvention will be described next with reference to FIG. 22. Similar tothe fifth embodiment, a characteristic feature of this embodiment isthat three objective lenses are mounted on a first movable member. Morespecifically, objective lenses 108a, 108b, and 108c are fixed/arrangedon a first movable member 105 at three positions separated from eachother by 120° with respect to a rotating shaft 107. Three magneticcircuits 112a, 112b, and 112c are fixed to a second movable member 106to be symmetrical about the rotating shaft 107. These objective lenses108a, 108b, and 108c and magnetic circuits 112a, 112b, and 112c arearranged at equal angular intervals on the same circumference around therotating shaft 107 as the center. In addition, three magnetic members200a, 200b, and 200c are bonded to the first movable member 105, andthree magnetic members 201a, 201b, and 201c, each consisting of an ironpiece, are embedded in the first movable member 105 at equal angularintervals.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

In this embodiment having the above structure, the same effects asdescribed above can be obtained by performing the same operation as thatin each embodiment described above. In the optical head of thisembodiment, since the three objective lenses can be switched and used inaccordance with the standards or specifications of a disk, a pluralityof special (different) optical heads suitable for the standards orspecifications of disks need not be prepared. Therefore, there isprovided an optical head which can properly process various data withoutrequiring any other optical heads.

Since pluralities of magnetic circuits and magnetic members are used,magnetic attraction forces acting on the first movable member can beeasily balanced. For this reason, the slide bearings are not pressedagainst the rotating shaft, and the frictional force, a so-called"rubbing", between the first movable member and the rotating shaft canbe minimized. This allows the first movable member to smoothly rotateand translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Ninth Embodiment!

An optical head according to the ninth embodiment of the presentinvention will be described next with reference to FIG. 23.

Similar to the sixth embodiment, a characteristic feature of thisembodiment is that four objective lenses are mounted on a first movablemember. More specifically, objective lenses 108a, 108b, 108c, and 108dare fixed/arranged on a blade 105a of a first movable member 105 at fourpositions separated from each other by 90° with respect to a rotatingshaft 107. Four magnetic circuits 112a, 112b, 112c, and 112d are fixedto a second movable member 106 to be symmetrical about the rotatingshaft 107. These objective lenses 108a, 108b, 108c, and 108d andmagnetic circuits 112a, 112b, 112c, 112d are arranged at equal angularintervals on the same circumference around the rotating shaft 107 as thecenter. In addition, four tracking coils 200a, 200b, 200c, and 200d arebonded to a first coil bobbin 105b, and four magnetic members 201a,201b, 201c, and 201d, each consisting of an iron piece, are embedded inthe coil bobbin 105b at equal angular intervals.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

In this embodiment having the above structure, the same effects asdescribed above can be obtained by performing the same operation as thatin each embodiment described above.

In the optical head of this embodiment, since the four objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of dedicated (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an optical head which canproperly process various data without requiring any other optical heads.

Since pluralities of magnetic circuits and magnetic members are used,magnetic attraction forces acting on the first movable member can beeasily balanced. For this reason, the slide bearings are not pressedagainst the rotating shaft, and the frictional force, a so-called"rubbing", between the first movable member and the rotating shaft canbe minimized. This allows the first movable member to smoothly rotateand translate.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, so-called "rubbing" can be minimized as in the abovecase.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Tenth Embodiment!

An optical head according to the tenth embodiment of the presentinvention will be described next with reference to the plan view of FIG.24 and the sectional view of FIG. 25.

A characteristic feature of this embodiment is that a first movablemember is different in shape from that in each embodiment describedabove. More specifically, elliptic holes 220a and 220b are formed at twopositions near the outer periphery of a first movable member 105. Inthis case, the positions where the holes 220a and 220b are formed aresymmetrical about a rotating shaft 107 and spaced apart from objectivelenses 108a and 108b by 90°.

Center yokes 221a and 221b to be inserted in the holes 220a and 220b arefixed to a second movable member 106. Permanent magnets 110a and 110b,yokes 111a and 111b, and the center yokes 221a and 221b constitutemagnetic circuits 112a and 112b. As shown in FIG. 25, the height of thecenter yokes 221a and 221b in the axial direction is set such that eachcenter yoke slightly protrudes (by, e.g., about 0.5 mm) from the lowersurface of a blade 105a of the first movable member 105. The length ofthe holes 220a and 220b in the rotating direction is set to be slightlylarger than that of the center yokes 221a and 221b in the rotatingdirection.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed.

In this embodiment having the above structure, although the structureand operation of the second movable member 106 are almost the same asthose in the fourth embodiment, the operation of the first movablemember 105 which is to be performed when the first movable member 105 iscoarsely moved in the tracking direction is different from that in thefourth embodiment. More specifically, if the first movable member 105 isto be coarsely moved in the tracking direction in the state shown inFIG. 25, the center yokes 221a and 221b are brought into contact withthe holes 220a and 220b. As a result, a required rotational amountcannot be obtained. For this reason, when the first movable member 105is to be coarsely moved in the tracking direction, a focus coil 109 isenergized first to finely move the first movable member 105 in the focusdirection so as to move it upward by a distance slightly larger than 0.5mm mentioned above. Tracking coils 200a and 200b are then energized toperform a tracking/driving operation. After the first movable member 105is rotated/driven to a necessary position, the focus coil 109 isdeenergized to lower the first movable member 105 so as to insert thecenter yokes 221a and 221b in the holes 220a and 220b. Such a series ofoperations are realized by supplying part of an output from theobjective lens selector 131 in the control section 126 in the signalprocessing system shown in FIG. 18 to not only the tracking controlcircuit 127 but also the focus control circuit 128.

By employing the above structure and operation, the height of the firstmovable member 105 in the axial direction (especially the thickness ofthe blade 105a) can be sufficiently reduced, and the overall profile ofthe unit can be reduced.

Assume that the first movable member 105 is rotated excessively, and anobjective lens 104 cannot be positioned on an optical path 141. In thiscase, excessive rotation of the first movable member 105 can beprevented by bringing the holes 220a and 220b into contact with thecenter yokes 221a and 221b. That is, the holes 220a and 220b and thecenter yokes 221a and 221b realize the function of a stopper. Even if,therefore, the first movable member 105 is rotated excessively, theobjective lens 104 can be quickly positioned on an optical path 124.

Note that buffer members such as rubber members may be arranged on thecontact surfaces between the holes 220a and 220b and the center yokes221a and 221b, or the contact surfaces may be shaped to allow surfacecontact (for example, the contact surfaces may be shaped into flatsurfaces). With this arrangement, the influences of vibrations, causedby collision, on objective lenses 104a and 104b, the focus coil 109, andthe tracking coils 200a and 200b can be minimized.

In the optical head of this embodiment, since the two objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of dedicated (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an objective lens driving unitwhich can properly process various data without requiring any otheroptical heads.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, the first movable member is balanced about therotating shaft. For this reason, so-called "rubbing" between the firstmovable member and the rotating shaft can be minimized. Therefore, finerotation and fine translation of the first movable member can besmoothly performed.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Eleventh Embodiment!

An objective lens driving unit according to the eleventh embodiment ofthe present invention will be described next with reference to FIG. 26.

A characteristic feature of this embodiment is that three objectivelenses are mounted on a first movable member, similar to the fifthembodiment. More specifically; objective lenses 108a, 108b, and 108c arearranged on a first movable member 105 at three positions spaced apartfrom each other by 120° with respect to a rotating shaft 107. Holes220a, 220b, and 220c are also formed in the first movable member 105.Three magnetic circuits 112a, 112b, and 112c are fixed to a secondmovable member 106 to be symmetrical about the rotating shaft 107, andcenter yokes 221a, 221b, and 221c are inserted in the holes 220a, 220b,and 220c. These objective lenses 108a, 108b, and 108c and magneticcircuits 112a, 112b, and 112c are arranged at equal angular intervals onthe same circumference around the rotating shaft 107 as the center.Three tracking coils 200a, 200b, and 200c and three magnetic members201a, 201b, and 201c, each consisting of an iron piece, are bonded tothe first movable member 105 at equal angular intervals.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

In this embodiment having the above structure, the same effects asdescribed above can be obtained by performing the same operation as thatin the tenth embodiment. In the optical head of this embodiment, sincethe three objective lenses can be switched and used in accordance withthe standards or specifications of a disk, a plurality of dedicated(different) optical heads suitable for the standards or specificationsof disks need not be prepared. Therefore, there is provided an opticalhead which can properly process various data without requiring any otheroptical heads.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, the first movable member is balanced about therotating shaft. For this reason, so-called "rubbing" between the firstmovable member and the rotating shaft can be minimized. Therefore, finerotation and fine translation of the first movable member can besmoothly performed.

Note that even if these objective lenses are arranged to be symmetricalabout the rotating shaft or arranged around the rotating shaft at equalintervals, the same effects as described above can be expected.

Twelfth Embodiment!

An optical head according to the twelfth embodiment of the presentinvention will be described next with reference to FIG. 27.

A characteristic feature of this embodiment is that four objectivelenses are mounted on a first movable member, similar to the sixthembodiment (FIG. 20). More specifically, objective lenses 108a, 108b,108c, and 108d are arranged on a blade 105a of a first movable member105 at four positions spaced apart from each other by 90° with respectto a rotating shaft 107. Holes 220a, 220b, 220c, and 220d are alsoformed in the blade 105a. Four magnetic circuits 112a, 112b, 112c, and112d are fixed to a second movable member 106 to be symmetrical aboutthe rotating shaft 107, and center yokes 221a, 221b, 221c, and 221d areinserted in the holes 220a, 220b, 220c, and 220d. These objective lenses108a, 108b, 108c, and 108d and magnetic circuits 112a, 112b, 112c, and112d are arranged at equal angular intervals on the same circumferencearound the rotating shaft 107 as the center. Four tracking coils 200a,200b, 200c, and 200d and four magnetic members 201a, 201b, 201c, and201d, each consisting of an iron piece, are bonded to the first movablemember 105 at equal angular intervals.

As a basic structure for supporting the first movable member 105 toallow it to move in the focus and radial directions, the same slidebearing mechanism as that in the fourth embodiment is employed. Inaddition, since the structure and operation of the second movable member106 are the same as those in the fourth embodiment, an illustration anddescription thereof will be omitted.

In this embodiment having the above structure, the same effects asdescribed above can be obtained by performing the same operation as thatin the tenth embodiment.

In the optical head of this embodiment, since the four objective lensescan be switched and used in accordance with the standards orspecifications of a disk, a plurality of dedicated (different) opticalheads suitable for the standards or specifications of disks need not beprepared. Therefore, there is provided an optical head which canproperly process various data without requiring any other optical heads.

Furthermore, since the objective lenses are positioned to cause thecenter of gravity of the first movable member to almost coincide withthe rotating shaft, the first movable member is balanced about therotating shaft. For this reason, so-called "rubbing" between the firstmovable member and the rotating shaft can be minimized.

Therefore, fine rotation and fine translation of the first movablemember can be smoothly performed. Note that even if these objectivelenses are arranged to be symmetrical about the rotating shaft orarranged around the rotating shaft at equal intervals, the same effectsas described above can be expected.

In the fifth, sixth, eighth, ninth, eleventh, and twelfth embodiments, acounterweight may be arranged in place of an objective lens on the firstmovable member. As is apparent from the plan views of FIGS. 28A, 28B,and 28C, the two objective lenses 108a and 108b and one counterweight222 are arranged such that the center-of-gravity position of the firstmovable member 105 almost coincides with the rotating shaft 107. Morespecifically, mass adjustment is performed by using the counterweight222 having a mass equal to the average value of the masses of the twoobjective lenses 108a and 108b. In other respects, the structures ofthese modifications shown in FIGS. 28A, 28B, and 28C are the same asthose of the fifth, eight, and eleventh embodiments.

Similarly, in each of the modifications shown in FIGS. 28D, 28E, and28F, the three objective lenses 108a, 108b, and 108c and onecounterweight 222 are arranged such that the center-of-gravity positionof the first movable member 105 almost coincides with the rotating shaft107. In other respects, the structures of these modifications are thesame as those of the sixth, ninth, and twelfth embodiments.

In each of the modifications shown in FIGS. 29A, 29B, and 29C, the twoobjective lenses 108a and 108b and two counterweights 222a and 222b arearranged such that the center-of-gravity position of the first movablemember 105 almost coincides with the rotating shaft 107. In otherrespects, the structures of these modification are the same as those ofthe sixth, ninth, and twelfth embodiments.

According to these modifications, although the numbers of objectivelenses mounted are smaller than those in the fourth to twelfthembodiments, respectively, the same effects can be expected.

In addition, the modifications shown in FIGS. 28B and 28D may employ amodification of the tracking drive operation of the first movable member105, which will be described below.

In the optical head shown in FIGS. 30A and 30B, a flexible print board223 extends from a side surface of the first movable member 105. One endof the flexible print board 223 is fixed to the first movable member105. The other end of the flexible print board 223 is fixed to a guideplate 224 extending vertically from the second movable member 106. Theflexible print board 223 is formed to be sufficiently long inconsideration of a displacement (trace deformation) upon rotation of thefirst movable member 105. Note that the flexible print board 223 servesto supply a current to the focus coil 109 and a tracking coil 200 and isconnected to the control system via the guide plate 224 and the secondmovable member 106. In addition, the side surface of the first movablemember 105 and the inner surface of the guide plate 224 are concentricwith respect to the rotating shaft 107 as the center, and the gap lengthbetween the surfaces is made constant.

In this modification, as is apparent from a change from the state inFIG. 30A to the state in FIG. 30B, the rotational angle of the firstmovable member 105 which is required to switch the objective lenses 108aand 108b is 120°. On the other hand, the required moving amount of theflexible print board 223 is about 60°, which is not larger than 1/2 therequired rotational angle of the first movable member 105. Therefore,this flexible print board 223 can be arranged between the magneticcircuits 112a, 112b, and 112c (arranged at almost 60°-intervals). Inthis arrangement, the magnetic circuits 112a, 112b, and 112c do notbecome obstacles.

In addition, the flexible print board 223 is deformed into a U-shape toalways apply a predetermined pressure (pressing force) to the firstmovable member 105 and the guide plate 224. This pressing force alwaysbiases the first movable member 105 in the direction of the rotatingshaft 107 regardless of a change in the rotational angle of the firstmovable member 105. For this reason, no pressure is applied to the firstmovable member 105 in the rotating direction, and no unnecessaryrestitutive force is generated upon rotation of the first movable member105. Therefore, tracking control is free from adverse effects.

With the above arrangement, a wiring pattern required to supply power tothe focus coil 109 and the tracking coil 200 can be easily andeffectively formed.

In addition, the same effects as described above can be expected fromthe movable member 105 having the two objective lenses 108a and 108b andthe two counterweights 222a and 222b as in the optical head shown inFIGS. 31A and 31B. In this modification, the rotational angle of thefirst movable member 105 which is required to switch the objectivelenses 108a and 108b is 90°, and the required moving amount of theflexible print board 223 is 45°. In this case as well, the flexibleprint board 223 can be arranged between the magnetic circuits 112a,112b, 112c, and 112d (arranged at almost 90°-intervals). In thisarrangement, the magnetic circuits 112a, 112b, 112c, and 112d do notbecome obstacles.

The same effects as those in the modification shown in FIGS. 30A and 30Bcan be expected from this modification.

Thirteenth Embodiment!

An optical head according to the thirteenth embodiment of the presentinvention will be described next with reference to FIGS. 32 to 35. FIG.32 is a plan view of the optical head. FIG. 33 is a sectional view takenalong a line A-A' of a first movable member in FIG. 32. FIG. 34 is asectional view taken along a line B-B' of the optical head in FIG. 32.FIG. 35 is a sectional view taken along a line C-C' of the optical headin FIG. 32.

In the optical head of this embodiment, the shape of each constituentelement is slightly different from that in each embodiment describedabove. This will be described in detail below.

A first movable member 105 includes a blade 105a having projections attwo positions with respect to a rotating shaft 107 as the center. Twoobjective lenses 108a and 108b are arranged to protrude from the blade105a at two positions spaced apart from these two projections by 90°.

As shown in FIG. 33, the objective lenses 108a and 108b are mounted atdifferent positions in the axial direction of the rotating shaft 107. Inthis case, the objective lens 108a located near a disk 101 has a largernumerical aperture (NA) than the objective lens 108b located far fromthe disk 101.

A rotating shaft bearing 105d is fixed in the center of the blade 105a.The rotating shaft 107 is engaged with the rotating shaft bearing 105d.With this arrangement, rotational movement of the blade 105a about therotating shaft 107 is allowed. Note that a circumferential groove isformed in the rotating shaft 107 at a position near the middle point inthe axial direction, thereby restricting translation of the blade 105ain the axial direction of the rotating shaft 107.

The upper and lower end portions of the rotating shaft 107 are rotatablyfitted to one end of a leaf spring 231a and one end of a leaf spring231b, respectively. The two leaf springs 231a and 231b are arranged tobe parallel to each other so as to constitute a parallel leaf springmechanism. The other end of each of the leaf springs is fixed to asecond movable member 106 via a fixing member 232. Therefore, the firstmovable member 105 can be translated in the axial direction of therotating shaft 107 while being suspended from the second movable member106 via the parallel leaf springs 231a and 231b. Note that the fixingmember 232 is inserted as a member for maintaining the parallelismbetween the leaf springs 231a and 231b.

The rotating shaft bearing 105d is manufactured by the following method.Outsert molding of a resin such as a plastic material is performed withrespect to the rotating shaft 107, and a clearance formed by thedifference in contraction ratio between the resin and the rotating shaft107 in this molding process is used as a small gap, thereby forming therotating shaft bearing 105d. By this manufacturing method, the rotatingshaft bearing 105d can be formed, which causes little backlash andprevents easy occurrence of aberrations due to a tilt of an objectivelens, thereby obtaining proper signals.

Since the structure and operation of the second movable member 106 arethe same as those in the first embodiment, a description thereof will beomitted.

In this case, the blade 105a is made of a rare-earth element or aneodymium magnet (or a plastic magnet consisting the same material) andis magnetized from the rotating shaft 107 toward the projections. Anannular yoke 233 having a substantially rectangular ring-like shape isformed around the blade 105a. Cylindrical tracking coils 200a and 200band booster coils 234a and 234b are alternately arranged on the middleportions of the respective sides of the yoke 233 so as to be woundtherearound. In the neutral state shown in FIG. 32, the projections ofthe blade 105a oppose the tracking coils 200a and 200b and the boostercoils 234a and 234b. In addition, rectangular focus coils 109a and 109b,each of which is two-dimensionally wound, are bonded to the surfaces ofthe tracking coils 200a and 200b. FIG. 35 (a sectional view taken alonga line C-C' in FIG. 32) shows the positional relationship between thetracking coils 200a and 200b and the focus coils 109a and 109b. Notethat the annular yoke 233 is fixed to the second movable member 106 viathe fixing member 232.

According to this embodiment having the above structure, the blade 105aitself is a magnetic member and part of a magnetic circuit. For thisreason, when focus coils 109a and 109b or the tracking coils 200a and200b are energized, a Lorentz force is generated. As a result, the firstmovable member 105 is slightly driven in the direction of thickness orradial direction of the disk 101.

In this embodiment, the parallel leaf springs 231a and 231b are used.Therefore, the first movable member 105 can be moved in the focusdirection without impairing the parallelism between the optical axes ofthe objective lenses 108a and 108b due to deformation of the parallelleaf springs 231a and 231b.

The first movable member 105 is moved in the tracking direction androtated about the rotating shaft 107 as in the fourth embodiment. Sincethe small gap between the rotating shaft bearing 105d and the rotatingshaft 107 is set to be 10 micron or less, a mount position offsetbetween the objective lenses 108a and 108b is set on a negligible level.

In addition, since the projections are formed at the two positions onthe blade 105a, when the objective lens 108 is guided onto an opticalpath 141, the two projections are located nearest to the yoke 233 tocoincide with the magnetic central position. Since a magnetically stablepoint is set when magnetic fields are present at the booster coils 234aand 234b as well as at the tracking coils 200a and 200b, accuratesynchronization can be established without using any means for measuringthe position of a magnetic pole, such as a Hall element, as in a generalmotor.

The same method as the method of instantaneously supplying a largecurrent to the tracking coils in the fourth embodiment is applied to thebooster coils 234a and 234b (i.e., a control signal from the objectivelens selector 131 in FIG. 18 is supplied to the booster coils 234a and234b) to generate kick pulses at predetermined intervals, therebyrotating the first movable member 105 at 90°-intervals.

Furthermore, since the permanent magnet and the coils are respectivelyarranged on the movable and stationary portions of the optical head, awiring pattern for supplying power to the coils can be easily formed.Therefore, the first movable member 105 can be easily rotated through180° or more. In addition, since the permanent magnet is used as theblade 105a, the rigidity of the optical head is high to obtain goodvibration characteristics, thus obtaining great practical effects.

A method of mounting the objective lenses will be described next. Thecenter axis of the parallel leaf springs 231a and 231b coincides with adirection perpendicular to a line segment connecting the centers of thetwo objective lenses 108a and 108b in the state shown in FIG. 32 (oneobjective lens 108a or 108b is on the optical path 141). As describedabove, the objective lens 108a is mounted at a level higher than that ofthe objective lens 108b. As shown in FIG. 33, while the parallel leafsprings 231a and 231b are in a neutral state, the upper surface of theobjective lens 108a is located above the lower surface of the upper leafspring 231a, and the objective lens 108b is located between the two leafsprings 231a and 231b.

At the same time, in this arrangement, movement of each objective lensis controlled such that the objective lens 108a is rotated in adirection in which it does not interfere with the leaf springs 231a and231b, and the objective lens 108b is rotated in the gap between the leafsprings 231a and 231b.

Letting L₁ be the operating range (maximum operating distance) of theobjective lens 108a, and L₂ be the operating range (maximum operatingdistance) of the objective lens 108b, L₂ is larger than L₁ inconsideration of interference with the leaf springs 231a and 231b. Adifference L between the levels at which the two objective lenses 108aand 108b are mounted is represented by

    L≦L.sub.2 -L.sub.1

When the objective lens 108a is used, the distance between the surfaceof the disk 101 and the objective lens 108a is the distance L₁, and thedistance between the objective lens 108b and the disk 101 is given by

    L.sub.1 +L

When the objective lens 108b is used, the distance between the surfaceof the disk 101 and the objective lens 108a is given by

    L.sub.2 -L

At this time, the distance between the objective lens 108b and the disk101 is the distance L₂.

In this case, L represents the difference between the levels at whichthe objective lenses 108a and 108b are mounted. When the difference L isa positive value, the objective lens 108a is closer to the disk 101 thanthe objective lens 108b. At this time, a minimum distance D to the firstmovable member 105 is given by

    D=MINIMUM (L.sub.1, L.sub.1 +L, L.sub.2 -L, L.sub.2)

If L₂ >L₁, then D=MINIMUM (L₁, L₁ +L, L₂ -L). If L<0, then D=L₁ +L<L₁.If 0<L≦(L₂ -L₁), then D=L₁. If L₂ -L₁ <L, then D=L₂ -L<L₁. As isapparent, when L is given by L≦L₂ -L₁, the minimum distance D ismaximized and coincides with the distance L₁.

The probability of collision between the objective lenses 108a and 108b,therefore, can be minimized by setting the difference L (between thelevels at which the objective lenses 108a and 108b are mounted) tosatisfy the above inequality.

Assume that the actual mounted states of the objective lenses 108a and108b contradict the neutral positions in the respective operatingranges. In this case, in order to correct such deviations, a DC currentmust be constantly supplied to position the objective lenses 108a and108b in the focus direction. In this embodiment, however, as describedabove, since the levels at which the objective lenses 108a and 108b areto be mounted are set in correspondence with the respective operatingranges, the power consumption of the unit can be reduced.

In addition, collision between the objective lenses 108a and 108b andthe disk 101 can be prevented, and damage such as flaws on the disk 101can be prevented.

As is apparent, a method of providing a deviation between the positionsof the objective lenses 108a and 108b in the optical axis direction isnot limited to the method of elastically supporting the first movablemember 105 with the parallel leaf springs 231a and 231b as in thisembodiment, but other methods such as an axial sliding method may beused.

Fourteenth Embodiment!

An optical head according to the fourteenth embodiment of the presentinvention will be described below with reference to FIGS. 36 to 39. FIG.36 is a plan view of the optical head. FIG. 37 is a sectional view takenalong a line A-A' of the optical head in FIG. 36. FIG. 38 is a partiallysectional view taken along a line B-B' of the optical head in FIG. 37.FIG. 39 is a sectional view taken along a line C-C' in FIG. 36.

This embodiment is different from the thirteenth embodiment in thestructure of a first movable member 105. The first movable member 105has a blade 105a at a position to oppose the surface of a disk 101, anda permanent magnet 240 fixed to the lower portion of the blade 105a. Inthis embodiment, the blade 105a is made of a composite materialconsisting of carbon and a resin having excellent slidingcharacteristics and high rigidity, such as a liquid crystal polymer, anepoxy resin, or a polyphenylenesulfite resin. As is apparent from thesectional view of FIG. 37, the permanent magnet 240 is formed into asubstantially elliptic shape with a hole 240a being formed in thecenter. The two ends of the permanent magnet 240 in the longitudinaldirection are magnetized to the N and S poles, respectively. Thepermanent magnet 240 is finished to be axially symmetrical. The blade105a and the permanent magnet 240 are integrally manufactured as thefirst movable member 105 by injection molding.

A rotating shaft 107 is constituted by a magnetic core 107a as a centralportion, and a coating portion 107b around the magnetic core 107a. Sincean intermediate portion of the magnetic core 107a, i.e., a fittingportion with respect to the permanent magnet 240, is large in diameter,magnetic fluxes flow more in this portion than in other portions of thepermanent magnet 240. Therefore, the neutral position of the firstmovable member 105 in the axial direction is magnetically determined.

As a material for the coating portion 107b, a composite resin consistingof a resin such as an epoxy resin, carbon, and mica is used. Byselecting such a material, the coating portion 107b has a high hardnessand excellent sliding characteristics.

FIG. 39 (a sectional view taken along a line C-C' in FIG. 36) shows thepositional relationship between tracking coils 200a and 200b and focuscoils 109a and 109b. In this embodiment, no booster coil is used, and alarge current is instantaneously supplied to the tracking coils 200a and200b as in the fourth embodiment.

An optical unit 120 (not shown) is not fixed to a movable member 104 butis fixed to a base 102 (a so-called separate optical system isemployed). For this reason, a laser beam LB is guided from the radialdirection of the disk 101 and deflected at 90° by a reflecting mirror142 fixed to a second movable member 106 so as to be guided to anobjective lens 108. As shown in FIG. 36, the focus coil 109a is partlybent to ensure the optical path of the laser beam LB from thisstationary optical system.

A magnetic flux flowing from the permanent magnet 240 to the focus coil109a (tracking coil 200a) passes through a U-shaped yoke 241 to form amagnetic path extending from the opposing focus coil 109b (tracking coil200b) to the permanent magnet 240. By using this magnetic path, theneutral positions of the objective lenses 108a and 108b in arecording/reproducing operation is determined.

A Lorentz force is generated by currents flowing in the tracking coils200a and 200b of the magnetic circuit constituted by the U-shaped yoke241 and the permanent magnet 240. As a result, the first movable member105 is finely driven in the direction of thickness and radial directionof the disk 101.

According to this embodiment having the above arrangement, the followingeffects can be obtained. In this embodiment, with only one permanentmagnet, the first movable member 105 can be driven in both the focus andtracking directions, and a driving force for switching the objectivelenses 108a and 108b can also be generated. Therefore, the number ofrelatively expensive permanent magnets used is decreased to reduce themanufacturing cost of the head.

In addition, for example, a coil opposing the S pole is located far awayfrom an end face of the reverse polarity, i.e., the N pole, so that amagnetic field of the S pole effectively acts on the coil. That is, theintensity of a magnetic field at a portion where an electromagneticinteraction between the permanent magnet and the coil occurs isincreased as compared with the case wherein two permanent magnets arebonded to oppose each other.

Furthermore, as in the tenth embodiment described above, since thepermanent magnet and the coil are respectively arranged on the movableand stationary portions of the unit, a wiring pattern for supplyingpower to the coil can be easily formed. In this embodiment, as in thefourth embodiment, since a shaft sliding method is used for a drivingoperation in the focus direction, the first movable member 105 may berotated clockwise or counterclockwise to switch the objective lenses108a and 108b. In principle, the first movable member 105 can be rotatedthrough 360°. The fourteenth embodiment realizes "switching of theobjective lenses by one-way rotation" which cannot be realized by any ofthe embodiments described above. Therefore, the possibility that theunit fails because of an operation error is greatly reduced.

Fifteenth Embodiment!

An optical head according to the fifteenth embodiment of the presentinvention will be described below with reference to FIGS. 40 to 42. FIG.40 is a sectional view of the optical head. FIGS. 41 and 42 are planviews showing the operation states of the optical head.

The fifteenth embodiment is different from the fourteenth embodiment ina support mechanism for a first movable member 105. More specifically, ahinge mechanism is employed for displacements in the axial direction ofthe first movable member 105 and around its axis. The positions wheretwo objective lenses 108a and 108b are mounted on the first movablemember 105 are very close to each other as compared with otherembodiments.

As shown in FIGS. 41 and 42, in this embodiment, one end of a firsthinge member 250 is fixed to the central portion of the first movablemember 105. The first hinge member 250 has a low-profile hinge 250a. Theposition of the hinge 250a coincides with the center-of-gravity positionof the first movable member 105. The first hinge member 250 is designedto allow rotation of the first movable member 105 within a finite anglerange.

The other end of the first hinge member 250 is fixed to one end of asecond hinge member 251. As shown in FIG. 40, the second hinge member251 has a four-joint hinge mechanism with hinges 251a and 251b arrangedat two positions. The other end of the second hinge member 251 is fixedto the second movable member 106 via a fixing member 232. The secondhinge member 251 is designed to allow translation of the first movablemember 105 in the axial direction.

Notches are formed near side portions of the first movable member 105,and focus coils 109a and 109b, each wound in the annular shape, arefitted/fixed in the notches. Rectangular tracking coils 200a and 200b,each wound two-dimensionally, are fixed on the surfaces of the annularfocus coils 109a and 109b. Centeryokes 221a and 221b are inserted in theannular spaces respectively defined by the focus coils 109a and 109b. Atthe neutral position of each selected one of the objective lenses 108aand 108b, the two opposing side portions of the tracking coils 200a and200b (portions extending vertically in FIG. 40) are located in amagnetic gap.

A magnetic member 252 made of an iron piece is mounted on the distal endportion of the first movable member 105. A yoke 253 and a permanentmagnet 254 are arranged to oppose the magnetic member 252 and fixed on asecond movable member 106. In this case, the yoke 253 has asubstantially U-shape with projections 253a and 253b formed at twopositions.

The two objective lenses 108a and 108b are fixed to the first movablemember 105 at positions close to each other. When the magnetic member252 opposes one projection 253b of the yoke 253, the objective lens 108ais positioned on the center axis (FIG. 41). When the magnetic member 252opposes the other projection 253a of the yoke 253, the objective lens108b is positioned on the center axis (FIG. 42). Note that in the statesshown in FIGS. 41 and 42, the objective lenses 108a and 108b arerespectively arranged on an optical path 141.

The operation of this embodiment will be described next.

The basic operation principle of the first movable member 105 is almostthe same as that of each embodiment described above. In this embodiment,the first movable member 105 is moved in the focus direction bydeforming the two hinges 251a and 251b of the second hinge member 251.When the first movable member 105 is to be moved in the trackingdirection, the hinge 250a of the first hinge member 250 is deformed.

In this case, the hinge 250a of the first hinge member 250 can berotated through about 10° in two directions with respect to the centeraxis, i.e., a total of about 20°. With this change in angle, the twoobjective lenses 108a and 108b can be switched.

While the objective lens 108a is in an operation state, the magneticmember 252 opposes one projection 253b. While the objective lens 108b isin an operation state, the magnetic member 252 opposes the otherprojection 253a. For this reason, the positions where the two objectivelenses 108a and 108b are used become magnetically stable points. In thiscase, the magnetic member 252 is located on the objective lens side withrespect to the first hinge member 250 and is located on the oppositeside to the four-joint hinge member 251. Therefore, magnetic attractionforces act in the directions in which the hinges 251a and 251b areextended by magnetic attraction. These directions are opposite to thedirections in which the hinges 251a and 251b are pushed, i.e., thehinges 251a and 251b are bent. For this reason, the overall firstmovable member 105 tends to restore the neutral position in the axialdirection. As a result, the driving characteristics in the focusdirection are greatly stabilized.

Sixteenth Embodiment!

An optical head according to the sixteenth embodiment of the presentinvention will be described next with reference to FIGS. 43 and 44.

This embodiment is different from the thirteenth embodiment in apositioning mechanism for objective lenses 108a and 108b. Morespecifically, in the fifteenth embodiment, the magnetic member 252 ismounted on the first movable member 105, and the permanent magnet 254 ismounted on the second movable member 106 via the yoke 253. In thesixteenth embodiment, a permanent magnet 254 is mounted on a firstmovable member 105, and a yoke 253 is mounted on a second movable member106.

Note that since the cross-section of the optical head of the sixteenthembodiment is almost the same as that of the fifteenth embodiment (seeFIG. 40), a description thereof will be omitted.

Magnetic sensors 255a and 255b such as Hall elements are fixed at thepositions where the projections 253a and 253b are formed. With themagnetic sensors 255a and 255b, which one of the objective lenses 108aor 108b is used (placed in an optical path 124) can be known. In thisarrangement, even if a strong shock is externally applied to the unit,an objective lens in an operation state can be discriminated. Therefore,great practical effects can be obtained. For example, an operation errorcan be prevented.

Seventeenth Embodiment!

FIG. 45 shows the arrangement of an optical head apparatus according tothe seventeenth embodiment of the present invention, which is roughlyconstituted by a stationary optical portion 401 and a lens actuatorincluding a rotating blade 402 as a movable support member and amagnetic circuit 411. The rotating blade 402 can be rotated in adirection parallel to the recording surface of a recording medium (to bereferred to as an optical disk hereinafter) (not shown) loaded in theoptical disk apparatus, and can also be moved in the direction of theoptical axis of a light beam irradiated on the optical disk. Thestationary optical portion 401 is constituted by a transmission opticalsystem including a light source 403 such as a semiconductor laser, acollimator lens 404, and a beam splitter 405, and a detection system,including a focusing lens 408, a holographic optical element (HOE) 409,and a photodetector 410, for detecting a light beam reflected by anoptical disk.

The rotating blade 402 has a cylindrical shape with a bottom, at leastthe upper end portion (in FIG. 45) of which is closed. A plurality of(two in this case) objective lenses 407a and 407b are arranged on theupper end portion of the rotating blade 402. The magnetic circuit 411 isconstituted by a pair of semi-arc yokes 412a and 412b arranged aroundthe rotating blade 402 at positions opposing each other at 180°, magnets413a and 413b attached to the inner circumferential portions of theyokes 412a and 412b, and tracking coils 414a to 414f arranged atpositions where they can oppose the magnets 413a and 413b of therotating blade 402. The arrangement and operation of this magneticcircuit 411 will be described in detail later.

A reflecting mirror 406 for forming an optical path between the beamsplitter 405 and the objective lenses 407a and 407b is arranged betweenthe stationary optical portion 401 and the rotating blade 402.

The operation of the optical head apparatus of this embodiment will bedescribed next. Light emitted from the light source 403 is collimated bythe collimator lens 404. The parallel beam is then focused by theobjective lens 407a or 407b via the beam splitter 405 and the reflectingmirror 406 to form a small beam spot on a surface, of an optical diskwhich is placed on the rotating blade 402 and rotated, on which data isrecorded (to be referred to as a recording surface hereinafter).

The light reflected by the recording surface of the optical disk travelsalong a route reverse to the above route, i.e., the route for incidentlight, from the light source 403 to the recording surface of an opticaldisk 420a or 420b through the collimator lens 404, the beam splitter405, the reflecting mirror 406, and the objective lens 407a or 407b.That is, the reflected light is reflected by the beam splitter 405through the objective lens 407a or 407b and the reflecting mirror 406and guided to the detection system. The detection system generates errorsignals for controlling the position of a small beam spot focused by theobjective lens 407a or 407b in the optical axis direction (focusdirection) and the radial direction of the optical disk 420a or 420b(tracking direction) with respect to a pit array on the recordingsurface of the optical disk 420a or 420b, and also reproduces areproduction signal recorded on the optical disk 420a or 420b.

The detection system for obtaining these three signals (the focus errorsignal, the tracking error signal, and the reproduction signal) can berealized by an arrangement like the one described in detail in "OpticalMemory Apparatus" in Japanese Patent Disclosure (KOKAI) No. 3-257.Although the detection system itself is irrelevant to the gist of thepresent invention, its operation will be briefly described below. Asdescribed above, the detection system in this embodiment is constitutedby the focusing lens 408, the HOE 409, and the photodetector 410. Lightreflected by an optical disk is focused on the photodetector 410 by thefocusing lens 408.

The region of the HOE 409 arranged between the focusing lens 408 and thephotodetector 410 is divided into two regions by a line extending in thesame direction as that of each track on the optical disk 420a or 420b.Holograms having different grating patterns are respectively formed inthese two regions of the HOE 409. More specifically, when one hologramhas a spindle-like grating pattern, the other hologram has a barrel-likegrating pattern. In addition, different grating pitches are set suchthat diffracted light beams of the respective holograms are incident onthe detection surface of the photodetector 410 at different positions.If the grating patterns of holograms on the HOE 409 are set in thismanner, light beams on the photodetector 410 exhibit characteristicchanges in shape in accordance with a focus offset. Therefore, thephotodetector 410 is constituted by two two-division light-receivingelements, and differential detection of the respective diffracted lightbeams is performed by the two-division light-receiving elements, therebydetecting a focus error. A tracking error can be detected from adifference between the diffracted light beams of the respectiveholograms. In addition, a reproduction signal can be easily detectedfrom the sum total of outputs from the photodetector 410. In thisembodiment, the detection system is constituted by the HOE. However, thepresent invention is not limited to this detection system, and any knowndetection optical system such as a focus error detection system based ona so-called astigmatism method using a combination of a focusing lensand a cylindrical lens can be equally used.

Four output signals output from the two two-division light-receivingelements constituting the photodetector 410 are input to a detectionsignal processor 501 to be amplified and arithmetically processed,thereby generating a reproduction signal, a focus error signal, and atracking error signal in the above manner. Of these signals, thereproduction signal is output to a signal processor (not shown) forperforming a decoding operation and the like. The focus error signal andthe tracking error signal are input to a control signal generatingcircuit 502 connected to a host system (not shown). After sequencecontrol to lock focusing servo control and signal processing such assuperposition of a special operation signal on a tracking control signalin a track search operation are performed, the resultant signals areoutput, as a focus control signal and a tracking control signal, from anactuator control circuit 503. Currents flowing in a focus coil 416 andthe tracking coils 414a to 414c in the magnetic circuit 411 arecontrolled in accordance with these focus and tracking control signals.

In accordance with driving forces generated by electromagnetic effectsupon this control, the rotating blade 402 is controlled in the opticalaxis direction (focus direction) of a light beam irradiated on anoptical disk and the radial direction (tracking direction) of theoptical disk, and control is performed to position a beam spot on atrack on the optical disk.

These arrangements and a series of these operations are basically thesame as those of a conventional optical head apparatus. A characteristicarrangement of this embodiment will be described below.

In general, an optical disk apparatus optically reads data recorded onan optical disk and reproduces the data as a signal. For this reason, ifdust and flaws are present on the recording surface of the optical disk,light is scattered, and data cannot be reproduced. For this reason, thethickness of a layer (generally a disk substrate) of an optical disk onwhich a light beam is incident is set to be large, and the size of abeam spot on the disk substrate surface is set to be large, therebyreducing the influences of dust and flaws produced after themanufacturing process. The disk substrates of many conventional opticaldisk generally have a thickness of 1.2 mm. However, when the numericalaperture of an objective lens is increased or the wavelength of lightemitted from a light source is shortened to increase the recordingdensity of an optical disk, drawbacks based on thick disk substratesbecome conspicuous.

FIGS. 1A and 1B show changes in transmission wavefront aberration asoptical disks tilt with respect to optical disks in cases wherein thethicknesses of the disk substrates are 1.2 mm and 0.6 mm, respectively.As shown in FIGS. 1A and 1B, even if the numerical aperture of theobjective lens remains the same, the transmission wavefront aberrationdue to a disk tilt is reduced, and the focusing characteristics of abeam spot on the recording surface are improved as the thickness of thedisk substrate decreases. For this reason, optical disks having thinnerdisk substrates have been developed. As a result, optical disks whosesubstrate thickness are different are present. It is inevitably requiredthat data be reproduced from these optical disks by using the sameapparatus. In order to meet such demands, the present invention has beenmade to stably reproduce data recorded on optical disks based ondifferent specifications associated with substrate thickness and thelike by using one simple, small, inexpensive apparatus without posingsuch conventional problems. This apparatus will be described in detailbelow.

FIGS. 46A and 46B schematically show how the specifications of opticaldisks are associated with the optical head apparatus. This caseexemplifies the two optical disks 420a and 420b having differentsubstrate thicknesses. The objective lenses 407a and 407b havingdifferent numerical apertures NAa and NAb are used for these opticaldisks 420a and 420b having different substrate thicknesses. The degreesof freedom in the specifications of the objective lenses 407a and 407bare associated with focal lengths (Fa and Fb), working distances (WDaand WDb), apertures (Da and Db), and the like. According to the degreesof freedom, several characteristic optical head apparatuses can beformed. This will be described in detail later.

In this embodiment, as shown in FIG. 45, the plurality of objectivelenses 407a and 407b respectively having optimal optical characteristicsin accordance with the specifications of optical disks are arranged onthe rotating blade 402. By selectively using these objective lenses,data can be reproduced from optical disks based on differentspecifications. If, for example, an optical disk to be used is a CD, thethickness of a disk substrate is set to be 1.2 mm, and the numericalaperture of an objective lens is set to be 0.45. If a recording mediumhaving a higher recording density is to be used, the thickness of a disksubstrate is set to be 0.6 mm, and the numerical aperture of anobjective lens is set to be 0.6. In this manner, an objective lens whichsatisfies these specifications is mounted. The rotating blade 402 isrotated in accordance with an optical disk inserted in the apparatus toselect the optimal objective lens to the optical disk, therebyperforming data reproduction. A control method of selecting one of theobjective lenses 407a and 407b will be described later.

FIGS. 47A and 47B show the shapes of objective lenses as examples. FIG.47A shows a glass mold lens. FIG. 47B shows a plastic injection lens.Although these lenses are only examples, they have characteristicdifferences in form because of different manufacturing methods andmaterials. Even with different specifications, lenses can be formed tohave the same outer shape or weight in this manner. If objective lenseshaving such a relationship are arranged, an unbalanced state of weightswhich degrades the vibration characteristics of an actuator does notoccur. Therefore, an excellent optical head apparatus can be formed.

FIG. 48 shows the detailed arrangement of a lens actuator constituted bythe rotating blade 402 and the magnetic circuit 411 (411a and 411b)shown in FIG. 45. The six tracking coils 414a to 414f, each having theshape shown in FIG. 49, are arranged on the outer surface of therotating blade 402. These tracking coils 414a to 414f constitute themagnetic circuits 411a and 411b, together with the magnets 413a and 413band the yokes 412a and 412b, so as to generate a driving force forselectively setting the objective lenses 407a and 407b on the opticalaxis of a light beam in accordance with the specifications of an opticaldisk (e.g., the substrate thickness of the optical disk) loaded in theoptical disk apparatus, and a driving force for rotating/controlling therotating blade 402 about a rotating shaft 415 as the rotational centerto follow a track offset caused by the decentering of the optical diskin reproducing data recorded on the optical disk. Assume that theoptical axis of a light beam is located on the chain line in FIG. 48.FIG. 48, therefore, shows a state wherein the objective lens 407b islocated on the optical axis of the light beam, and the light beam isirradiated on the optical disk via the objective lens 407b, therebyreproducing data from the optical disk.

In this case, tracking control for data reproduction performed byirradiating a light beam on and optical disk via the objective lens 407ais performed by using the tracking coils 414d and 414e in the magneticcircuit 411a and the tracking coils 414a and 414b in the magneticcircuit 411b. On the other hand, tracking control for data reproductionperformed by irradiating a light beam on an optical disk via theobjective lens 407b is performed by using the tracking coils 414e and414f in the magnetic circuit 411a and the tracking coils 414b and 414cin the magnetic circuit 411b.

In this embodiment, the objective lenses 407a and 407b are spaced apartfrom each other by 60°, and the tracking coils 414a to 414f are arrangedat 60°-intervals around the entire circumference of the rotating blade402. The relative positional relationship between the objective lensesand the tracking coils is set such that the hollow portion of eachtracking coil 414 shown in FIG. 49 coincides the objective lenses 407aand 407b. With this arrangement of the objective lenses 407a and 407band the tracking coils 414a to 414f, two tracking coils can always beset in each of the magnetic circuits 411a and 411b regardless of whichone of the objective lenses 407a and 407b is used for data reproduction.With this arrangement, four of the six tracking coils 414a to 414f areused for tracking control. That is, the efficiency in using the trackingcoils is high, and a large driving force can be efficiently generated.

FIG. 50 shows the arrangement of the lens actuator in more detail. Inthe rotating blade 402 of the lens actuator, ferromagnetic pieces 419ato 419d are respectively embedded between the tracking coils 414a and414b, the tracking coils 414b and 414c, the tracking coils 414d and414e, and the tracking coils 414e and 414f. These ferromagnetic pieces419a to 419d serve to determine the neutral position of the rotatingblade 402 in the optical axis direction of a light beam and the rotatingdirection of the rotating blade 402 with respect to the rotating shaft415 as the center by using a magnetic attraction force acting betweenthe magnets 413a and 413b in the magnetic circuits 411a and 411b. Wheneach of the objective lenses 407a and 407b is located on the opticalaxis of a light beam, two of the ferromagnetic pieces 419a to 419d arerespectively located at the centers of the magnetic circuits 411a and411b. More specifically, when the objective lens 407a is located on theoptical axis, the ferromagnetic pieces 419a and 419c are respectivelylocated in the magnetic circuits 411a and 411b. When the objective lens407b is located on the optical axis, the ferromagnetic pieces 419b and419d are respectively located in the magnetic circuits 411a and 411b, asshown in FIG. 50.

Since the ferromagnetic pieces 419a to 419d are arranged to be locatedin the magnetic circuits 411a and 411b to determine the neutral positionof the rotating blade 402 in this manner, the neutral position of therotating blade 402 can be determined at the optimal positions for thetwo objective lenses 407a and 407b. Note that in an arrangement fordetermining a neutral position by using an elastic member such as arubber member, the neutral position is present at only one point. Unlikein this embodiment, therefore, neutral positions cannot be set at twodifferent positions. In addition, a method of determining neutralpositions by using a magnetic balancing force as in the embodiment isdisclosed in "Objective Lens Driving Unit" in Japanese Patent Disclosure(KOKAI) No. 60-140549. In this prior art, however, determination of onlyone set of neutral positions is disclosed, but determination of aplurality of sets of neutral positions is not disclosed.

With the use of the lens actuator having the above arrangement, one ofthe objective lenses 407a and 407b can be arbitrarily located on theoptical axis of a light beam by controlling the waveforms of currentssupplied to the tracking coils 414a to 414f. FIG. 51 is a timing chartfor explaining a control method of selecting one of the objective lenses407a and 407b in the lens actuator shown in FIG. 50. More specifically,FIG. 51 shows the waveforms of currents to be supplied to the trackingcoils 414a to 414f when the objective lens 407a is replaced with theobjective lens 407b, and the objective lens 407b is replaced with theobjective lens 407a. FIG. 49 shows the direction of a current flowing ineach of the tracking coils 414a to 414f, and the direction of a force(indicated by "407b→407a" and "407a→407b") generated by each of thetracking coils 414a to 414f. Assume that when a current flows in each ofthe tracking coils 414a to 414f clockwise as shown in FIG. 49, thedirection of the current is represented by a symbol "+", and a forceacts on the rotating blade 402 to rotate it clockwise in this state.

When the objective lens 407b is to be replaced with the objective lens407a, currents of the same direction are supplied to each of pairs oftracking coils spaced at 180°, i.e., the pair of tracking coils 414a and414d, the pair of tracking coils 414b and 414e, and the pair of trackingcoils 414c and 414f. Of these currents, the currents supplied to thepair of tracking coils 414b and 414e and the pair of tracking coils 414cand 414f are stepwise currents whose directions are reversed from "+" to"-" or from "-" to "+", as shown in FIG. 51. This operation is similarto a lens actuator control operation called "track jump" which isperformed to repetitively reproduce data from the same track on anoptical disk. In this embodiment, however, a characteristic feature ofthis operation is that the rotational angle of the rotating blade 402 islarge. Another characteristic feature is that the waveforms of currentssupplied to the tracking coils 414b and 414e are the same when theobjective lens 407a is replaced with the objective lens 407b. This isbecause the positions of the tracking coils 414b and 414e located in themagnetic circuits 411a and 411b change every time the objective lenses407a and 407b are replaced with each other.

A tracking control signal for supplying these currents to the trackingcoils 414a to 414f is generated by the control signal generating circuit502 in accordance with a request from the host system, as shown in FIG.45, and is supplied to the tracking coils 414a to 414f via the actuatorcontrol circuit 503.

As described above, according to this embodiment, the plurality ofobjective lenses 407a and 407b are mounted on the same lens actuator. Bycontrolling the waveforms of currents supplied to the tracking coils414a to 414f, the objective lenses 407a and 407b are selectively set onthe optical axis of a light beam in accordance with optical disks basedon different specifications so as to be used for reproduction of datafrom these optical disks. With this arrangement, only one optical headis required. This solves the problems posed in the conventionaltechniques of mounting a plurality of objective lenses on specialoptical heads or lens actuators, respectively, i.e., the problem thatthe actuators or the optical heads occupy a large space, or the merit ofreproducing data from optical disks based on different specifications byone optical disk apparatus is impaired because an optical system cannotbe shared.

Eighteenth Embodiment!

FIG. 52 schematically shows the arrangement of a lens actuator of thisembodiment. In the embodiment, objective lenses 407a and 407b arearranged on a rotating blade 402 to be point symmetrical with a rotatingshaft 415 as the center. Stationary optical portions 401, each having anarrangement similar to that shown in FIG. 45, are arranged incorrespondence with these objective lenses 407a and 407b.

The optical head apparatus of this embodiment is mounted to be movablein the radial direction (indicated by an arrow A) of an optical disk 420when the optical disk 420 is fitted on a guide shaft 418 of a spindlemotor 417 to be loaded. The rotating blade 402 is arranged such thatwhen the optical head apparatus is moved in the direction indicated bythe arrow A, the locus of a rotating shaft 415 coincides with a straightline (indicated by the chain line) passing through the center of theoptical disk 420. A data pit array 510 on the optical disk 420 is readby being irradiated with a light beam emerging from the objective lens407a or 407b.

In this case, in order to select and use an objective lens suitable forthe optical disk 420 loaded in the optical disk apparatus, signalsdetected from the optical disk 420 via the objective lens 407a or 407bneed only to be selected as signals (a focus control signal and atracking control signal) for driving the lens actuator in accordancewith an instruction from a host system. For this reason, an objectivelens need not be selected by rotating the rotating blade 402 through alarge angle of, e.g., 60°, as in the seventeenth embodiment. Therefore,in this embodiment, the lens actuator may have almost the samearrangement as that of a lens actuator having one objective lens mountedthereon. That is, a lens actuator having the two objective lenses 407aand 407b mounted thereon can be easily formed as an application of aconventional technique.

Nineteenth Embodiment!

FIG. 53 shows the arrangement of an optical head apparatus according tothe nineteenth embodiment of the present invention, in which the twostationary optical portions 401 in the eighteenth embodiment (FIG. 52)are fixed/arranged separately from a carriage for moving the opticalhead apparatus in the radial direction of an optical disk 420.

The arrangement of this embodiment will be described below. A pickup 421carrying a movable optical system constituted by objective lenses 407aand 407b and a reflecting mirror (not shown) is arranged on the lowersurface side of the optical disk 420. Two stationary optical systems 401are arranged on the extended line of the path of the pickup 421 in thecircumferential direction of the optical disk 420. A light beamirradiated from each stationary optical system 401 toward the pickup 421is reflected at a right angle by the reflecting mirror of the movableoptical system and focused/irradiated on the optical disk 420 via theobjective lens 407a or 407b. A light beam reflected by the optical disk420 passes through the objective lens 407a or 407b and is deflectedhorizontally by the reflecting mirror to be sent to a corresponding oneof the stationary optical systems 401. When data is to be reproducedfrom the optical disk 420, a light beam focused/irradiated on theoptical disk 420 via the objective lens 407a or 407b isintensity-modulated in accordance with the presence/absence of a pit456, and the reflected light passes through the objective lens 407a or407b and is guided to a corresponding one of the stationary opticalsystems 401 by the reflecting mirror.

The pickup 421 has a carriage 460 which can be moved in the radialdirection (indicated by an arrow A) of the optical disk 420, i.e., thetracking control direction, by using a linear motor 474 as a drivesource. A plurality of support rollers 462 are arranged, as roller pairseach supported through a leaf spring, on the two side portions of thecarriage 460. These support rollers 462 are brought into rolling contactwith two guide shafts 464 arranged horizontally and parallelly along theradial direction of the optical disk 420 so as to be movably supportedin the radial direction of the optical disk 420.

In addition, radial coils 466 are mounted on the two side portions ofthe carriage 460. These radial coils 466 are fitted on inner yokes 468of a magnetic circuit. The inner yokes 468 are connected to outer yokes470. Magnets 472 are mounted on the inner sides of the outer yokes 470,thereby constituting the linear motor 474.

In this case, when power is supplied to the radial coils 466, a thrustis generated to reciprocate the carriage 460 in the radial direction ofthe optical disk 420.

According to the arrangement of this embodiment, as the components ofthe optical head apparatus on the carriage 460, only the lens actuatorand the reflecting mirror are required, so that the number of componentsmounted on the carriage 460 can be greatly decreased. Therefore, theoptical head apparatus is capable of high-speed access.

Twentieth Embodiment!

FIG. 54 shows the arrangement of an optical head apparatus according tothe twentieth embodiment of the present invention. The same referencenumerals in the twentieth embodiment denote the same parts as in thenineteenth embodiment, and a description thereof will be omitted. In thenineteenth embodiment (FIG. 53), the two objective lenses 407a and 407bare arranged to be used for optical disks based on differentspecifications and hence cannot be used at once. Therefore, there is noneed to have the stationary optical systems 401 respectivelycorresponding to the objective lenses 407a and 407b, and one stationaryoptical system may be designed such that many components are commonlyused for the two objective lenses.

This embodiment is designed from this viewpoint. More specifically, theembodiment is designed such that a light beam from a stationary opticalsystem 401 is selectively guided to one of the objective lenses 407a and407b by an optical switch constituted by, e.g., a polarization planerotating element 431 and a polarization beam splitter 432 in accordancewith the specifications of an optical disk 420 loaded in the apparatus.As the polarization plane rotating element 431, one of the followingelements can be used: an element designed to control the rotationalamount of the polarization plane of a light beam incident via a capsulehaving a cholesteric material sealed therein and transparent electrodesmounted on the upper and lower surfaces of the capsule by controlling anapplied voltage; and an element designed to electrically control therotational amount of the polarization plane of an incident light beam byusing the magnetooptical effect of an optical crystal.

As described above, since the optical head apparatus of this embodimentrequires only one stationary optical system, the overall arrangement ofthe stationary optical system can be further simplified, and theobjective lenses can be selectively used for reproduction of data fromoptical disks based on different specifications with substantially thesame arrangement as that of a conventional optical head apparatusconstituted by one objective lens and one stationary optical system.

21st Embodiment!

FIG. 55 shows the arrangement of an optical head apparatus according tothe 21st embodiment of the present invention, in which the arrangementof the movable optical system mounted on the carriage 460 of the opticalhead apparatus of the nineteenth embodiment (FIG. 53) is furthersimplified to improve the high-speed access characteristics.

More specifically, in each of the seventeenth to twentieth embodiments,the two objective lenses 407a and 407b are arranged on the rotatingblade 402 capable of two-dimensionally controlling the positions of theobjective lenses. In contrast to this, in this embodiment, two objectivelenses 407a and 407b are fixed on a movable end of a carriage 434 whichis constituted by a suspension constituted by, e.g., two parallel leafsprings and can be controlled (moved) only in the optical axisdirection, thereby simplifying the arrangement of the lens actuator.With this arrangement, a reduction in the weight of the movable memberin an access operation is achieved to realize an access operation at ahigher speed.

In addition, in this embodiment, a magnetic circuit 435 for moving theobjective lenses 407a and 407b in the optical axis direction is attachedto a magnetic circuit 437 for moving the carriage 434 in the radialdirection of an optical disk 420.

With this arrangement, the components on the carriage 434 are furtherreduced in weight. In this embodiment, since the controllable degree offreedom of the lens actuator is set for only one axis, a mechanismcapable of performing control in the direction of the remaining one axis(control in the tracking direction) is required. For such a mechanism, aswing mirror 430 may be arranged at a light beam exit portion directedfrom the stationary optical system 401 to the movable optical system soas to control the position of a beam spot on the optical disk 420 in theradial direction. Furthermore, similar to the twentieth embodiment shownin FIG. 54, an optical switch constituted by a polarization planerotating element 431 and a polarization beam splitter 432 may bearranged to share the arrangement of the stationary optical system 401.

The manner of setting specifications for objective lenses with respectto optical disks based on different specifications in each of theseventeenth to 21st embodiments will be described below with referenceto FIGS. 56 and 57. The optical disk 420 is mounted on the spindle motorwith a surface on which a light beam is incident being considered as areference surface. For this reason, as shown in FIG. 56, if a differencebetween the specifications of the optical disks 420a and 420b is adifferent in substrate thickness, the range in which the rotating blade402 is moved in the optical axis direction of a light beam can beminimized by setting objective lenses having different focal lengths buthaving almost the same working distance as the two objective lenses 407aand 407b. With this arrangement, even if the optical disks 420a and 420bare replaced with each other, focus control can be easily performed tofocus a light beam on the recording surface of the optical disk.

Assume that optical disks using polycarbonate as a substrate materialand respectively having thicknesses of 1.2 mm and 0.6 mm as the opticaldisks 420a and 420b, and the focal length of the objective lens 407bused for reproduction of a signal from the optical disk 420b is set tobe 2.6 mm. In this case, if the focal length of the objective lens 407aused for reproduction of a signal from the optical disk 420a is set tobe 3 mm, working distances WDa and WDb of the objective lenses 407a and407b can be made substantially the same.

FIG. 57 shows a method of coping with not only different thicknesses ofthe substrates of the optical disks 420a and 420b but also differentdensities of data recorded thereon. Assume that the optical disk 420a isa CD on which digital music data is recorded, and is based onspecifications for the next generation, which is higher in recordingdensity than the optical disk 420b. In this case, the numerical apertureof the objective lens 407a for reproduction of a signal from the opticaldisk 420a is 0.4 to 0.45, and that of the objective lens 407b forreproduction of a signal from the optical disk 420b is 0.6, which islarger than the numerical aperture of the objective lens 407a.

If apertures Da and Db of the objective lenses 407a and 407b are set tobe the same, the coefficients of utilization of incident light beamsbecome the same. Therefore, the detection levels of reproduction signalsobtained by detecting light beams reflected by the optical disks 420aand 420b can be made substantially the same. This allows simplificationof the arrangement of the detection signal processor 501 in FIG. 45. Ifdetection signals obtained by the photodetector 410 change in leveldepending on optical disks subjected reproduction processing, theamplification degree must be controlled to make the reproduction outputlevels become almost the same value. Such control is required for thefollowing reason. If the detection level changes, the control gains ofthe focus control system and the tracking control system change,resulting in unstable control.

If the focal length of the objective lens 407b is set to be 2.6 mm, theapertures Da and Db of the objective lenses 407a and 407b can be madeequal by setting the focal length of the objective lens 407b to be 3.9mm. That is, as shown in FIG. 57, a stepped portion is formed on aportion, of the rotating blade 402, which serves to support theobjective lenses 407a and 407b so that the objective lenses 407a and407b can be disposed at different distances from the optical disk inaccordance with the focal lengths of the objective lenses 407a and 407b.If specifications for the two objective lenses 407a and 407b are setunder such conditions, since the outer shapes and weights of the lensescan be made substantially the same, although the numerical apertures aredifferent, the weight balance of the lens actuator fordriving/controlling the objective lenses two-dimensionally is improved.As a result, a lens actuator with excellent controllability can beeasily realized.

FIG. 58 shows an adjustment means used when the two objective lenses407a and 407b are not properly mounted on the rotating blade 402. Assumethat numerical apertures NAa and NAb of the two objective lenses 407aand 407b are represented by NAa<NAb. Prior to a description of thisadjustment means, the background will be described with reference toFIG. 59.

FIG. 59 shows changes in transmission wavefront aberration caused whenoptical disks tilt relative to objective lenses. A curve D representsthe characteristics of the objective lens 407a having a smallernumerical aperture, whereas a curve C represents the characteristics ofthe objective lens 407b having a larger numerical aperture. As isapparent, the influence of a tilt on the objective lens 407a having thesmaller numerical aperture is smaller than that on the other objectivelens. By using this characteristic, the optimal adjustment method isdetermined.

The adjustment method will be described below with reference to FIG. 58,although no detailed description is required due to the descriptionassociated with FIG. 59. Relative tilt adjustment with respect to anoptical disk is performed by using the objective lens 407b having thelarger numerical aperture. In this case, the optical disk 420a isarranged in a tilted state with respect to the objective lens 407ahaving the smaller aperture. However, since the influence of this tilton the objective lens 407a is smaller than that on the objective lens407b, reproduction of a reproduction signal can be performed properly asa whole.

Although particular embodiments have been described above, the presentinvention can be carried out by arbitrarily combining the aboveembodiments. In this case, further many effects can be expected. Thegist of the present invention is to provide an optical head apparatuswhich can obtain reproduction signals having sufficiently high qualityin reproducing signals from optical disks based on differentspecifications, without considerably changing an optical head apparatusconstituted by one objective lens, by selectively using at least twoobjective lenses suitable for the specifications of the optical disks,which are arranged on a lens actuator.

As has been described above, according to the present invention, since apredetermined objective lens can be selected (and used) from a pluralityof objective lenses suitable for different types of recording media inaccordance with the type of a recording medium used, proper datareproduction can always be performed regardless of the specifications ofa recording medium. In addition, according to the present invention,especially since a plurality of objective lenses are mounted on amovable support member such as a rotating blade, and one of theobjective lenses is selected by controlling the movable support member,only one lens actuator is required. Therefore, the overall arrangementof the apparatus can be greatly reduced in size and simplified ascompared with an arrangement having optical heads respectively havingobjective lenses based on different specifications for optical headsbased on different specifications, and head moving mechanisms.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the present invention in its broaderaspects is not limited to the specific details, representative devices,and illustrated examples shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents. For example, it has been described that theplural objective lenses are provided for processing a plurality ofoptical disks based on different standards associated with, e.g.,recording density, allowable warp value, and substrate thickness.However, the present invention is not limited to this. If differentspecifications are set for objective lenses in a recording operation anda reproducing operation, respectively, with respect to the same opticaldisk, the plural objective lenses may be selectively used for arecording operation and a reproducing operation, respectively. Further,the optical disk is not limited to the read-only optical disk, but maybe a write-once type optical disk or a rewritable optical disk.

What is claimed is:
 1. An optical head apparatus used for an opticaldata recording/reproducing device, comprising:plural movable objectivelenses for irradiating light in an optical path of a common light sourceonto a recording medium; and means for selecting a desired objectivelens among said plural objective lenses and moving the selected desiredobjective lens to locate the selected desired objective lens in theoptical path of the common light source to receive light from the commonlight source and irradiate the received light through the selecteddesired objective lens onto the recording medium.
 2. An apparatusaccording to claim 1, wherein said plural objective lenses areassociated with types of plural recording media; andsaid selecting meanscomprises means for selecting the desired objective lens in accordancewith the type of the recording medium.
 3. An apparatus according toclaim 1, wherein said plural objective lenses comprises a firstobjective lens suitable for recording and a second objective lenssuitable for reproducing; andsaid selecting means comprises means forselecting one of said first and second objective lenses depending on arecording mode or a reproducing mode.
 4. An apparatus according to claim1, wherein said plural objective lenses are associated with types ofsignal processings for plural recording media; andsaid selecting meanscomprises means for selecting an objective lens in accordance with thetype of the signal processing of the recording medium.
 5. An apparatusaccording to claim 1, which further comprises:means for holding saidplural objective lenses, said holding means being movably around an axisperpendicular to the recording medium.
 6. An apparatus according toclaim 5, wherein said holding means holds said plural objective lenseswith an equal interval around the axis.
 7. An apparatus according toclaim 5, wherein said holding means holds the plural objective lenseswith unequal intervals around the axis.
 8. An apparatus according toclaim 5, wherein said holding means holds said plural objective lenseshaving focal distances such that distances between said objective lensesand the data recording medium become constant.
 9. An apparatus accordingto claim 1, wherein said plural objective lenses are mounted on arotatable member such that said plural objective lenses are at an equaldistance from a rotation axis of said rotatable member.
 10. An apparatusaccording to claim 1, wherein said plural objective lenses havedifferent optical characteristics.
 11. An optical head apparatus usedfor an optical data recording/reproducing device, comprising:a movablemember driven in a direction of thickness of a recording medium and adirection perpendicular to the direction of thickness, the movablemember having a common light source emitting light in an optical path ofthe common light source; plural movable objective lenses, mounted onsaid movable member and movable by movement of said movable member, forirradiating light from the optical path of the common light source ontothe recording medium; and means for selecting a desired objective lensin accordance with a type of the recording medium, and moving saidmovable member to locate the desired objective lens in the optical pathof the common light source to receive light from the common light sourceand irradiate the received light through the selected desired objectivelens onto the recording medium.
 12. An apparatus according to claim 11,wherein said movable member is supported by a slide bearing mechanismfor allowing said movable member to slide in an axial direction androtate about an axis of said movable member.
 13. An apparatus accordingto claim 12, wherein said plural objective lenses are mounted on saidmovable member with equal intervals around the axis of said slidebearing mechanism.
 14. An apparatus according to claim 12, wherein saidplural objective lenses are mounted on said movable member at an equaldistance from the axis of said slide bearing mechanism.
 15. An apparatusaccording to claim 12, wherein said plural objective lenses are mountedon a rotatable member such that a center of gravity of said pluralobjective lenses is set to coincide substantially with an axis of saidrotatable member.
 16. An apparatus according to claim 11, wherein saidplural objective lenses have different optical characteristics.
 17. Anapparatus according to claim 11, whereinsaid movable member is supportedby a slide bearing mechanism for allowing said movable member to slidein an axial direction and rotate about an axis of said movable member;and said objective lenses are mounted on said movable member withunequal intervals around the axis of said slide bearing mechanism. 18.An apparatus according to claim 11, wherein said selecting meanscomprises tracking coil means for driving said movable member in thedirection of thickness and the direction perpendicular thereto.
 19. Anapparatus according to claim 11, wherein said selecting means comprisescoil means, fixed to said movable member, for driving said movablemember in the direction of thickness and the direction perpendicularthereto.
 20. An apparatus according to claim 11, wherein said movablemember is supported by a slide bearing mechanism for allowing saidmovable member to slide in an axial direction and rotate about an axisof said movable member, andsaid movable member can be rotated about theaxis through at least (360/n)°, where n is the number of said pluralobjective lenses.
 21. An apparatus according to claim 11, whereinsaidmovable member is supported by a slide bearing mechanism for allowingsaid movable member to slide in an axial direction and rotate about anaxis of said movable member; said objective lenses are mounted on saidmovable member with equal intervals around the axis of said slidebearing mechanism; and said selecting means comprises:coil means fordriving said movable member at least around the axis; and magneticcircuit means, arranged at equal intervals around said movable member,for applying magnetic field to said coil means.
 22. An apparatusaccording to claim 21, wherein said magnetic circuit means comprisesmagnetic circuits, the number of the magnetic circuits being equal tothe number of said objective lenses.
 23. An apparatus according to claim11, whereinsaid movable member is supported by a slide bearing mechanismfor allowing said movable member to slide in an axial direction androtate about an axis of said movable member; and said selecting meanscomprises:magnetic members arranged around the axis of said movablemember; and magnetic circuits, arranged at equal intervals around saidmovable member, for applying magnetic fields to said magnetic members.24. An apparatus according to claim 23, wherein said magnetic membersare arranged at equal intervals around the axis of said movable member.25. An apparatus according to claim 11, wherein said movable member issupported by a slide bearing mechanism for allowing said movable memberto slide in an axial direction and rotate about an axis of said movablemember, and said movable member comprises at least one counterweight forbalancing masses of said objective lenses around the axis of saidmovable member.
 26. An apparatus according to claim 25, wherein saidobjective lenses and said counterweight are arranged at equal intervalsaround the axis of said movable member.
 27. An apparatus according toclaim 25, whereinsaid selecting means comprises magnetic circuits forgenerating a driving force of said movable member; and the number ofsaid objective lenses and said counterweight is equal to the number ofthe magnetic circuits.
 28. An apparatus according to claim 11, whereinsaid movable member is supported by a slide bearing mechanism forallowing said movable member to slide in an axial direction and rotateabout an axis of said movable member, and said movable member comprisesprojections protruding in a radial direction.
 29. An apparatus accordingto claim 11, wherein said movable member is supported by a slide bearingmechanism for allowing said movable member to slide in an axialdirection and rotate about an axis of said movable member, and saidmovable member comprises a cylindrical portion on one side thereof withrespect to the axis and a portion protruding more in a radial directionthan the cylindrical portion on the other side thereof.
 30. An apparatusaccording to claim 29, wherein said selecting means comprises:coilmeans, fixed to the cylindrical portion of said movable member, fordriving said movable member at least around the axis; and magneticcircuit means, arranged to oppose the cylindrical portion of saidmovable member, for applying magnetic field to said coil means, themagnetic circuit means being arranged at a lower position than theprotruding portion.
 31. An apparatus according to claim 11, whereinsaidmovable member is supported by a slide bearing mechanism for allowingsaid movable member to slide in an axial direction and rotate about anaxis of said movable member; said objective lenses are arranged at equalintervals around the axis of said movable member; said selecting meanscomprises:coil means for driving said movable member at least around theaxis; and magnetic circuit means for applying magnetic field to saidcoil means; and said movable member comprises holes into which a part ofsaid magnetic circuit means is inserted.
 32. An apparatus according toclaim 31, wherein said magnetic circuit means comprises magneticcircuits, the number of the magnetic circuits being equal to the numberof the holes and the parts of said magnetic circuits are respectivelyinserted into the holes.
 33. An apparatus according to claim 11,whereinsaid movable member is supported by a slide bearing mechanism forallowing said movable member to slide in an axial direction and rotateabout an axis of said movable member; said objective lenses are arrangedat equal intervals around the axis of said movable member; saidselecting means comprises:first coil means for driving said movablemember around the axis; second coil means for driving said movablemember in the axial direction; and magnetic circuit means for applyingmagnetic field to said first and second coil means; said movable membercomprises holes into which a part of said magnetic circuit means isinserted; and a drive of said movable member around the axis isperformed after a drive of said movable member in the axial direction.34. An apparatus according to claim 11, whereinsaid movable member issupported by a slide bearing mechanism for allowing said movable memberto slide in an axial direction and rotate about an axis of said movablemember; said objective lenses are arranged at equal intervals around theaxis of said movable member; said selecting means comprises:coil meansfor driving said movable member around the axis; an arcuated guide plateextending around said movable member; and a flexible printed circuitboard for coupling said movable member to said guide plate and allowingsupply of a current to said coil means.
 35. An apparatus according toclaim 11, whereinsaid movable member is supported by a slide bearingmechanism for allowing said movable member to slide in an axialdirection and rotate about an axis of said movable member; saidobjective lenses are arranged at equal intervals around the axis of saidmovable member; said selecting means comprises:coil means for drivingsaid movable member around the axis; magnetic circuits for applyingmagnetic fields to said coil means; an arcuated guide plate extendingaround said movable member to have a length corresponding to at least((360/n)/2)°, where n is the number of said magnetic circuits; and aflexible printed circuit board for coupling said movable member to saidguide plate and allowing supply of a current to said coil means.
 36. Anapparatus according to claim 11, in which said movable member has amagnet, and which further comprises coil means, arranged around saidmovable member, for driving said movable member at least in thedirection perpendicular the direction of thickness.
 37. An apparatusaccording to claim 36, wherein said movable member comprises projectionsprotruding in a radial direction.
 38. An apparatus according to claim37, wherein said coil means comprises:an annular yoke surrounding saidmovable member; and a coil fixed to said yoke.
 39. An apparatusaccording to claim 38, wherein said yoke has a non-circular shape. 40.An apparatus according to claim 11, wherein said movable member iselastically supported by leaf springs in a direction of thickness of therecording medium.
 41. An apparatus according to claim 11, whereinsaidmovable member is supported by a slide bearing mechanism for allowingsaid movable member to slide in an axial direction and rotate about anaxis of said movable member; the slide bearing mechanism is elasticallysupported by leaf springs and allowed to move in an axial direction; andobjective lenses are mounted on said movable member such that at leastone of said objective lenses can move between said leaf springs.
 42. Anapparatus according to claim 11, wherein said selecting meanscomprises:a non-circular magnet fixed to said movable member; a yokearranged around said movable member; and coil means, fixed to a portionof said yoke which is adjacent to said magnet, for driving said movablemember at least in the direction perpendicular to the direction ofthickness.
 43. An apparatus according to claim 11, whereinsaid movablemember is elastically supported by a hinge mechanism to be movable atleast in the direction perpendicular to the direction of thickness; andsaid objective lenses are mounted on said movable member within an anglerange in which said hinge mechanism is elastic.
 44. An apparatusaccording to claim 43, wherein said hinge mechanism comprises twohinges.
 45. An apparatus according to claim 43, whereinsaid selectingmeans comprises magnetic circuit means capable of magnetically holdingsaid movable member at two positions in the direction perpendicular tothe direction of thickness; and said objective lenses are locatedbetween said magnetic circuit means and said hinge mechanism.
 46. Anoptical head apparatus used for an optical data recording/reproducingdevice, comprising:a stationary optical system including a light sourcefor emitting light in an optical path and a detection system fordetecting light reflected by a recording medium, and arranged at aposition fixed to the recording medium; plural movable objective lensesfor focusing/irradiating light emitted from said light source into saidoptical path onto the recording medium; a movable support membersupporting said plural movable objective lenses and arranged to bemovable in a direction parallel to the recording medium, said pluralobjective lens being movable by means of said movable support member;and control means for controlling said movable support member to movesaid movable objective lenses and selectively locate a desired one ofsaid plural objective lenses into said optical path to receive lightfrom said stationary light source and irradiate the received lightthrough the selected desired objective lens onto the recording medium.47. An apparatus according to claim 46, whereinsaid movable supportmember is movable in a direction parallel to the recording medium; andsaid control means controls a length of movement of said movable supportmember.
 48. An apparatus according to claim 46, whereinsaid movablesupport member is rotatable in a direction parallel to the recordingmedium; and said control means controls an angle of rotation of saidmovable support member.
 49. An apparatus according to claim 48,whereinsaid movable support member comprises a ferromagnetic piece; saidcontrol means comprises:magnetic circuit means for rotating said movablesupport member, the positioning of said movable support member withrespect to the rotation being performed by locating the ferromagneticpiece in the magnetic circuit means; and means for supplying a currentto said magnetic circuit means to rotate said movable support member.50. An apparatus according to claim 49, whereinsaid magnetic circuitmeans comprises tracking coil means, mounted on an outer surface of saidmovable support member, for tracking light on the recording medium; andsaid control means supplies a given current to said tracking coil meansto apply a larger rotating force to said movable support member than ina tracking operation so as to attract said movable support member to arotational position determined by a magnetic positioning action of saidferromagnetic piece, thereby selectively locating a desired one of saidobjective lenses on the optical axis.
 51. An apparatus according toclaim 48, wherein said plural objective lenses are arranged with equalintervals around a rotation axis of said movable support member.
 52. Anapparatus according to claim 46, wherein said stationary optical systemincludes plural optical systems corresponding to said plural objectivelenses.